Here is a build I've been fooling around with for a while now. It's not really optimized, but it'll let you approximate an Illithid's abilities at level 8.
[spoiler]
Human PsyWar 1/Aberrant Paragon 1/PsyWar 4/Aberrant Paragon 2 (Dragon 332)
1-Illithid Heritage
H-Illithid Skin
1B-Illithid Grapple
Flaw-Illithid Grapple
Flaw-Illithid Grapple
3-Illithid Legacy
3B- Traded in for Mantled Warrior ACF: The Planes
6-Illithid Grapple
6B-Illithid Extraction
Powers (ML 7):
1-Stomp, Grip of Iron, Astral Traveler, Psionic Charm
2-Psionic Levitate, Read Thoughts, Pick any two powers.
3-Astral Caravan (Aberrant Paragon has Knowledge: The Planes as a class skill)
Note: It's not printed in the article, but errata states that Aberrant Paragon's HD are D8's.
Variations:
[spoiler]I don't care about planar travel!
Human PsyWar 2/Aberrant Paragon 3/PsyWar 1
1-Illithid Heritage
H-Illithid Skin
1B-Illithid Grapple
Flaw-Illithid Grapple
Flaw-Illithid Grapple
2B-Illithid Grapple
3-Illithid Extraction
6-Illithid Legacy
[/spoiler]
[spoiler]Gestalt = True Illithid
PsyWar 1/Aberrant Paragon 1/PsyWar 4/Aberrant Paragon 2
Psion (Telepath) 8
1-Illithid Heritage
H-Illithid Skin
1B-Illithid Grapple
1B-Illithid Grapple
Flaw-Illithid Grapple
Flaw-Illithid Grapple
3-Illithid Extraction
3B- Traded in for Mantled Warrior ACF: The Planes
5B- Traded in for Telepathic Communication ACF
6-Illithid Skin (Hyperconscious alternative: Mental Adversary)
6B-Illithid Skin (or Overwhelm Buffer)
[/spoiler]
For the uninitiated, Aberrant Paragon provides two levels of class feature advancement (restricted to a list, but PsyWar manifesting is included), darkvision 120ft, aberration type, +2 constitution and a choice between +2 charisma or +2 strength and -2 charisma.
[/spoiler]
As ADMG mentioned, Complete Psionic has stats for Larval Flayers, which are tadpoles that grow too large to be implanted in a brain. They tend to be destroyed because they can't become normal Illithids anymore, only Neothelids, but they're CR 1 and might make a decent (improved) familiar.