Book of Vile Darkness: some lore on Juiblex, nothing on Zuggtmoy
Using the answer from this question as a starting point, I looked into the Book of Vile Darkness (for 3e, not 4e like that answer says; there is a similar book for 4e, but it doesn't appear to contain very much about demon lords, whereas the 3e one does, so I assume that's what the other answer meant), and found this about Juiblex on page 134:
Juiblex, known as the Faceless Lord, is a loathsome demon of slime and ooze. Even most demons shun him, and the demon princes are said to refer to him contemptuously as the “lord of nothing.” He is among the weakest demon lords but is a terrifying foe nonetheless. He embodies many of the horrible abilities of various slimes, oozes, and puddings, and he commands impressive magical powers as well.
The domain of Juiblex is his by right of power—he has driven everything from the Slime Pits except the various slimes and oozes that teem there. Nevertheless, a few demons—
hezrous, mainly—pay him enough fealty that they bring victims for Juiblex and his slimy brood to hunt and feed on.
So it seems that Juiblex isn't very popular among demons, and does tend to associated mostly with oozes, but in addition to the Alkiliths I found in my question, this suggests that Hezrous also associate with Juiblex.
Page 136 also contains a reference to a Herzou working for Juiblex:
Juiblex has many slime, pudding, ooze, and jelly “servants,” although none are intelligent enough to serve the demon lord willingly—except for one.
Darkness Given Hunger is the largest black pudding known. It was possessed by a hezrou demon at Juiblex’s command, and then an imprison possessor spell was cast upon
the fusion, making it permanent. For centuries, the demon has dwelled within the pudding, and the two have truly become one in the foul depths of the Abyss. Now, Darkness Given Hunger is Juiblex’s main servant, helping patrol the Abyssal layer upon which they both dwell, looking for food.
However, I have found nothing on Zuggtmoy in this book.
Fiendish Codex I - Hordes of the Abyss: less lore on Juiblex, more on Zuggtmoy
This 3.5e book includes more lore on Zuggtmoy. The lore on Juiblex is pretty much the same as the above (except without mentioning Hezrou, so not of interest to this question), although it does include this in his stat block on page 67:
Summon Tanar’ri (Sp) Once per day, Juiblex can automatically summon 3d10 dretches, 1 hezrou, or 1 alkilith (Fiend Folio 46). This ability is the equivalent of a 9th-level spell (CL 20th).
So this confirms Alkilith (from my question) and Hezrou (from the above source) and adds Dretches to the list of demons associated with Juiblex.
The lore on Zuggtmoy says this on page 80:
Zuggtmoy has no fear of combat. Given the opportunity to smash and ruin living flesh, she rarely backs down. She is seldom encountered without a contingent of fungus monsters and vrocks, whom she uses as a buffer against melee fighters while she spends the first few rounds of combat casting [...]
And just above that on page 79, in her stat block:
Summon Tanar’ri (Sp) Once per day, Zuggtmoy can automatically summon 1d4 vrocks. This ability is the equivalent of a 9th-level spell (CL 20th).
So Vrocks associate with Zuggtmoy; there's also an image of an "arrow demon of Zuggtmoy" in that book, but I can't find any information about it outside of that picture's caption. An arrow demon appears to be a thing defined outside of this book in other 3.Xe material.
Here's the picture of the "arrow demon of Zuggtmoy" from "Fiendish Codex I - Hordes of the Abyss":
In addition, the Forgotten Realms wiki page on Zuggtmoy claims that she
could field powerful demons of varying strengths.
with a reference to "Fiendish Codex I - Hordes of the Abyss", but I couldn't find where it was drawing this information from myself in that book.
Temple of Elemental Evil (AD&D 1e module): Further information on Zuggtmoy
Thanks to @KorvinStarmast for pointing me in this direction; this adventure module heavily features Zuggtmoy, but there are few mentions of demons in relation to her. However, I have managed to find the following:
In area 353, p. 93, various precious stones are mentioned.
Each stone is attuned to a demon: a Type I to each of the least value; Type II to those of 100 gp; Type III to those of 500 gp; Type IV to those of 1,000 gp; and babau demons to those of 5,000 gp.
I'm not familiar enough with AD&D to know what Types I-IV mean, but babau demons are at least listed explicitly, and there must be various other demons that are associated with her as per these "Types".
Furthermore, her stat block on p. 123 describes her ability to summon demons:
it summons (01 -50) 1-4 Type I demons, (51-75) 1-3 Type II demons, (76-90) 1-2 Type III demons, 'or (91-00) 1 babau demon.
As in the previous quote, it mentions these demon Types and mentions the babau demon explicitly.
Magazines: Dungeon Magazine #118/Dragon Magazine #337
Dungeon Magazine #118 has a small section called "Demonomicon of Iggwilv: Juiblex, the Faceless Lord", which has a little information on page 7:
Pod demons gather in small colonies, herding oozes, while rupture demons of all sizes hide here and there.
However, I'm not sure what "pod demons" or "rupture demons" are, maybe this was more of a 4e thing...
Dragon Magazine #337 has a large section called "Demonomicon of Iggwilv: Zuggtmoy, Queen of Fungi", which mentions a demon called a Vathugu repeatedly, which is described in depth within this section as well. Page 52 offers this picture of them:
Page 54 gives us a short list of demons, though:
The inhabitants of Shedaklah [Zuggtmoy's layer of the Abyss] are mostly demons. Vrocks are common in the skies above, and vathugus and hezrous stalk the bogs below. Chasmes and rutterkin can be encountered with some frequency as well.
So that's Vrocks (these seem to be the favourites so far, besides fungi, obviously), vathugus, hezrous, chasmes and rutterkin, in addition to the vrocks and babau above.