Mike,
It is a little different here in the UK, there is an abundant supply of materials that can be had for very little money or for free, but you do have to work for it.
We have a large number of model engineers per square mile here and you soon become adept at accepting overspill as long as you reciprocate the offer. It was only recently that I was given about 30 sash weights (UK made sash weights are good for cast iron, I don't think the US made ones are any good, so I have been told).
In your case, I would go around friends, neighbours and relatives and explain what you are doing and then ask to have a root around in their garages and sheds to see if they have stuff squirreled away, say left over from grandads days, they are usually glad to get rid of it. The other thing is to ask people not to throw anything that might be useful away, let you see it before being discarded. You can get lots of good materials out of old photocopiers and printers etc. But don't expect them to take back what you don't want, it will be up to you to dispose of the leftovers. I had a neighbour throwing away an old baby cot, I got loads of 1/4" steel rod out of it. It can be surprising what can be found in discarded rubbish, even old big bolts can give you a nice piece of tensile steel.
Good luck on your search
John