1) Actually make your own sounds from scratch, you're going to need money. Especially for studio equipment, props n stuff to make your own authentic sounds.
2)Download some decent software, i would say money comes into play but these days no one pays for anything on the internet. Create sounds with programs.
3)This is probably the best for you. Rip sounds from TV/DvD/VHS/Downloads/Games. Anything you can get your hands on. Or you can edit existing sounds, like the ones already in the folder.
Some programs i use are Sound Forge for audio editing and Psound to take sounds directly from a PS/2 disc.
Furthermore, just curious, what sounds are you dissatisfied with? I've pretty much overhauled the whole sound folder for 1.2 and i don't want to miss anything.