Maybe it's because I've only been here for a few days, but I haven't seen anything regarding online stores or their reputation, costs/deals (however you want to look at it), and things of that nature. I'm aware of the unspoken agreement that members will naturally go to each other for parts before looking to outside sources, but I doubt anyone's got Nismo's revamped s15 6-speed lying around waiting for the guy who's mad because his silvia's stock 6-speed couldn't handle the torque he put out.
Anyway, the site I've got most of my parts from is FRSport. If you've never been there, I'd suggest at least giving it a look. It's a site founded by mostly Nissan (see: s-chassis) enthusiasts.
I got my one-piece driveshaft from The Driveshaft Shop. If you need or want a new driveshaft for your s-chassis, they have both ABS and non-ABS driveshafts for s13's and s14's, made of either steel or aluminum.
I'd post links to the sites, but I'm too wet behind the ears around here, apparently
If any of you have 'go-to' sites for hard to find parts, I'd like to hear them, and I'm sure the other members would as well.
I wasn't sure if I should post this in the general or market sub-forum, but I figured this would be a safer bet.