John and all,
I am a member of our Acquissions committee and have to admit that we are not as pro=active as we might be. But most professional museums will at least answer the phone or e-mail.
Something that has not been mentioned yet is the historical societies; most of which do not own equipment. Nearly every Fallen Flan railroad has a society remembering it. Some are small and others quite large, like the B&O Historical Society.
Remember too that you will usually have to sign an agreement that allows the org, society or library to displse (sell) your stuff in order to benifit the collection.
Further, you can be sure that you will not get a permanent display agreemeent for anything. It is just not practical.
don't under estimate your stuff, the smaller the railroad the more likely it is a one of a kind item. Paper from the SP or the UP exists by the ton
but Northwestern Pacific is much scarcer.
Ted Miles