The way PGMusic implemented loops is very clever.. The import loop dialog lets you manually enter the info that would normally be embedded in the header of a commercial loop... so the upshot is that you can make a loop out of ANY sound snippet!

Therefore you can search the web for sounds... and there are literally millions of downloadable sounds, musical and otherwise. Just google the phrase "free sounds

Also, if there is a sound you like in a song you have on CD, you could use a WAV editor to isolate that sound and save it as a snippet that can be looped