When I get some spare time (nyuk!), I'll post some sources for some of the springs and the roll pins from bulk suppliers like McMaster and Fastenal. There's not much special about the compression springs for the detents and the roll pins - gunnies can buy them in huge bulk.
Some people try to shove things like pipe cleaners and such down a gas tube to clean it. I personally think this is a mistake. If someone really wants to clean a gas tube, pull it out of the rifle and soak it in something like MPro-7 to soften up the carbon, then spray brake cleaner through the tube.