You can try running free ads on Craigslist looking for old trains. Most of the calls I get are crap, but every now and then something nice comes along.
Another avenue to find trains locally are the clubs. TCA is the big one. If there are TCA members in your area you might visit with them. The TTOS has broken up into a lot of local clubs. Your local hobby shops might be able to put you in touch.
I cannot stress how important it is to meet people with trains. The best way to learn about trains is to see them and hold them.
You might see collectors advertising to buy trains on craigslist or selling trains on eBay. (You Can search eBay just in a 100 mile radius with the ADVANCED link to the right of the search button most ebay pages
