You can use another manifester's powers
Not really an item, per se, but a way of gaining more powers without leveling up or spending feats.
See the PFSRD:
Manifest an Unknown Power from Another's powers Known
A psionic character can attempt to manifest a power from a source other than his own knowledge (usually another willing psionic character).1 To do so, the character must first make contact (a process similar to addressing a power stone, requiring a Spellcraft check against a DC of 20). A psionic character can make contact with only a willing psionic character or creature (unconscious creatures are considered willing, but not psionic characters under the effects of other immobilizing conditions). Characters that can’t use power stones for any reason are also banned from attempting to manifest powers from the knowledge of other psionic characters. Mental contact requires 1 full round of physical contact, which can provoke attacks of opportunity. Once contact is achieved, the character becomes aware of all the powers the other character knows up to the highest level of power the contactor knows himself. Next, the psionic character must choose one of the powers and make a second Spellcraft check (DC 15 + the power’s level) to see if he understands it. If the power is not on his class list, he automatically fails this check.
Upon successfully making contact with another willing psionic character or creature and learning what he can of one power in particular, the character can immediately attempt to manifest that power even if he doesn’t know it (and assuming he has power points left for the day). He can attempt to manifest the power normally on his next turn, and he succeeds if he makes one additional Spellcraft check (DC 15 + the power’s level). He retains the ability to manifest the selected power for only 1 round. If he doesn’t manifest the power, fails the Spellcraft check, or manifests a different power, he loses his chance to manifest that power, although he does not spend any power points unless he successfully manifests a power.
Whether this process results in a successful manifestation of a power or not, the entire process must be performed every time a character wants to manifest a power from another’s powers known.
So either take powers from your friends, or knock out enemy manifesters and carry them around. Keeping them unconscious is fairly easy; just apply some Ability Drain on their Intelligence, Wisdom, or Charisma to get it to 0, and they can't wake up until someone magically restores it. Then the only tricky part is keeping them in a way that's portable and accessible, without having to lug them around. The recent question about trapping people may be useful, though do note that it is for 3.5; some details may be different in Pathfinder.
Also, be aware that this process is not exactly quick; you need several Spellcraft checks and it takes a few rounds.
Get the Student's Surge
The Student's Surge gives you four extra Expanded Knowledge feats (as well as Psicrystal Affinity), which is a really nice expansion of your power repertoire. May require some retraining, though.
Restore this ability to Power Stones
I want to point out that in the 3.5 version of these rules, the parenthetical marked 1 above said "usually a power stone or another willing psionic character" (emphasis mine), which allowed for power stones to be used with your own power points to avoid burning the stones. Unfortunately, this option seems to have been removed. Probably because it never really made sense with the rest of the section, which is constantly talking about the "character or creature" and never again mentions the stones.
Thus the cost of gaining another power known was power level × manifester level × 25 gp, but do note that the process of accessing the power was fairly time-consuming, as is accessing another's power. Plus the stone could be used like a scroll if you were out of power points/didn't have time to do the whole thing.
Homebrew a psionic version of the Page of Knowledge
Spells and powers are pretty similar (spells typically being a bit better, particularly lower-level spells that scale automatically with caster level while powers require more power points spent), so the same cost of (power level)2 × 1,000 gp seems pretty fair, or at least as fair as the Page of Knowledge is. I suggest some kind of stone or crystal, in keeping with the themes of psionics. Power Crystal, perhaps? Make it seem like a refinement of the power stone.