Clutchs for automatics can really only be found at tranny shops (as far as I know. I haven't ever seen any online

). They have some stronger made ones that those that come in your stock tranny.
And your tranny already has wear on it. New ones alone will be an improvement alone. As for upgrading gears, you can modify your gear ratio. And there are also stronger made gears. Differen metals... Made different ways.
I wish I could go into more detail on how each is different, but I haven't studied it enough lately. The best suggestion I have is drop into a few different tranny shops in your area and see what they offer. I don't really know how many places will carry upgrades. But there is always something stronger than stock.. The torque converter is ther really big thing. Most places should be able to do that for you.
I'll try to do some research and get back to you if I can. Good luck on your search. (Hope Tony weighs in soon)
-Mike