(I’m not an expert in this.) Here’s some info about the computer junk universe.
Electronic Waste Recycling Act of 2003: Covered Electronic Waste Payment System (SB 20/SB 50) established the EWaste business. It collects taxes on products, and distributes payments for collecting product for recycling. The state’s friendly website with info is at eRecycle.org.
You can beg for parts at: Trash Nothing (directory of junk exchangers), LAReUseIt, LA Freecycle, Craigslist’s Free and Computer listings.
You can buy parts on Ebay or Craigslist, of course.
Other ways to find them are to poke around dumpsters and behind buildings. People leave old computers out for scavengers.
For surplus parts and new parts check out Apex Electronics, All Electronics, ITC Electronics, Marvac, Frys, Pacific Radio, Electronic City. These tend to be expensive.
(LA Dumpster Dive does free food… but maybe they’d have other things.)