Does anyone know which adventures have Illithids? I am looking for a tier two adventure or one for levels 7-9 in other editions.
"Adventure Lookup" lists 25 modules containing illithids, although a number of them are re-releases of the classic first edition GDQ series.
In G3 (first edition, Hall of the Fire Giant King) there was a chamber on the third level (cave level, more like a 'dungeon' then part of the Hall proper) with a group of illithids who are there observing the drow - they have little affect on the plot or story arc. This encounter is then repeated in G1-3 (first edition), GDQ1-7 (first edition), Against the Giants: The Liberation of Geoff (second edition) and Against the Giants (fifth edition, as contained in Tales of the Yawning Portal).
In D3 (first edition, Descent into the Depths of the Earth, there is a second illithid observation point. This one is more significant, as one of only three planned encounters for the module. The illithids have wererat minions , a drow prisoner, and substantial treasure. This encounter is reprinted in GDQ1-7 (first edition).
S3 Expedition to the Barrier Peaks features a single illithid as the BBEG for the adventure on the deepest level of a crashed spaceship. If you are looking for spelljammer connections this module has many tie-ins, but the illithid itself is not particularly well-developed. I keep a campaign journal of one of my games, so if you are interested in how that adventure could play out you might have a look. It is pretty true to the first edition original but adapted for fifth edition rules; the module starts in Post 157.
I do not have first hand experience with any of the other modules listed, but many of them appear to have illithids as much more central elements rather than one-off encounters.
Waterdeep Dragon Heist for 5e
The hard part for your request is the tier of play. Mind flayers are pretty nasty, so adventures that sport them as an entire faction tend to be higher level. For example Waterdeep: Dungeon of the Mad Mage, has an entire level dedicated to them, but it is for character level 14, well beyond your tier 2 or level 7-9 target.
Waterdeep: Dragon Heist does have a prominent Mind Flayer in one of its factions. The recommended range just barely touches tier 2 towards the end, but as the villain lair for this faction sports Xanathar himself as a possible opponent, it should not be an issue to play this adventure with a higher level group. We ran a heist mission against Xanathar's operation with 7th level characters, had a blast of fun doing it, and barely made it out alive. And that mind flayer with his kaggle of Intellect Devourers was a scary, scary opponent, that nearly killed two of our characters, and made our escape very difficult.