There aren't really many patches for character sprites, but inserting new ones is pretty easy, if you find any good sprites that you like and are free to use. Now for graphics, there should be a few in the ROM Hacking Resources thread in the ROM Hacking section, so look around and you'll find some.
Personally, if you're making your own hack. I think you should try and learn how to do these things yourself once you have the time, in the summer perhaps.