If you are looking for wav and midi sounds
Just have a look on this site that has some.
If you want to convert midi into wav, just watch for midimeow in the left menu. And if you want to convert from wav into midi you will need a pay software (a pay software but the result may be very different in function of the settings you are using, because the midi format doesn't allow to do a conversion like you could do ti like for mp3 for example.)
Here is a software that does the job:
Midi to wav maker