See if you can't become an outsider so you can PaO into one. Neraphim (from the Planar Handbook) are LA +0 outsiders, as are humanoids with the Otherworldly feat. Also, star elves.
Planetars have Int 22, and are 14 HD creatures. Balors have 20 HD (so, probably a bit out of your league), and 24 Int. Nalfeshnee have Int 22 and are 14 HD. Ice devils (gelugons) are 14 HD and 22 Int. Pit fiends (probably the one you'll want to go after, if you can make the UMD check) have 18 HD and 26 Int.
If you aren't naturally an outsider (for a given value of 'natural'), then find a way to cast it on yourself twice in a row to make it a permanent duration buff.
Then just do the standard thing with age categories (+3), level ups (+5 by level 20), tomes and/or
wish abuses (+5; you can get infinite
wishes as soon as you get access to
lesser planar binding), items (+6), and potentially PrCs (check the
crystal master and similar). I'm sure there are other ways, as well.