Nintendo 64 emulatio is rather new and far from perfected. Not to mention the ROMs are almost impossible to find.
About 1 out of 500 website saying the have ROMs actually have them. For the emulators i use project 64. It works
with most games with few glitches. None of the other emulators work on my computer. http://www.romhustler.net
has all the games you will need. The only problem is that it wasn't working the last time I went there.
I don't know of any other sites that have games.
Remember, you need a fast computer to play these games.