A very long time ago there was a trading section on these forums (it predates my ever posting here, in fact, and that's been a LONG time). Unfortunately, some folks used it as an opportunity to scam people, hurt feelings and thrown pottery were had, and this being the official forums from the game's publisher (FanPro at the time) it was felt that a trading/sales forum was a bad idea, lest the company be held legally responsible for a bad transaction.
Hope that clears it up a little. As Wikkid said though, there's a number of good places on Facebook and other places to find the parts you need- and if you come up short, start a thread here explaining what you're looking for and I know many of us are always happy to help you come up with ideas for proxy replacements.