Depends on how you define "find"... I can start by telling you where you can buy/import them. Piano arrangements of Terra and Eyes on Me can be found in the FF6 and FF8 OST piano books, I believe
GameMusic.com still carries them. Otherwise they're printed by
DoReMi, you can import directly from them at reasonable prices. And if you're looking for the sheet music to the Piano Collections, I think you can find these too at GameMusic.com, though they aren't exactly cheap ($20 per book). Personally I imported these straight from Japan, though they're slightly more of a hassle.
Now, if you're looking for online scans of said music, then maybe you could try
Final Fantasy Music Online.
I usually don't approve of people downloading for free what you normally buy, but I can also see why you would be unwilling to cough up some serious money if you're only interested in a few of the songs. If you want the whole OSTs though, then I'd much rather see that purchase the books; supporting Square, Nobuo Uematsu, and last but not least your eyes (the books are
much easier to play from). Thank you.
Hope that helps, and have a nice day.