You can still try any of the more popular P2P programs for the PC, select sound effects for download, and then just be sure to scan them with your AV program prior to using. The mere action of downloading selected P2P files do not "give" anyone a virus - it's executing a bad file. That said, most sound effects you are looking for are in excess of 50Mb, so after downloading arrange your files by size and delete those that are small in size. Also, do not click on any file you've downloaded that doesn't have a .MP3 extension.
I haven't looked for sound effects here, but one place I DO download MP3's from, from free (no registration or anything required) is
HTTP://beeMP3.com There is no www. preceding. Happy Hunting!