Those cars aren't very popular in terms of performance upgrades. My understanding is that there was a turbo engine offered but not here in the States. I would recommend an engine swap to something like the 200 hp 3S-GTE. However, here's a link that might help you.
http://www.toysport.com/
They are off the 405 just south of LAX. I haven't been there myself but I remember my brother used to order Celica stuff from there years ago. Other than that, check with a few import shops in your area and see what they say. Also, check Tercel forums. Toyota Nation has a pretty big one. Good luck.