A modest suggestion from a lurker here on this topic...

A group of N Scalers have used Trovestar to put together an online database of more than 40,000 items, including some 30,000 pieces of rolling stock and 10,000 locomotives that have been produced in N Scale.   This is a "crowdsourced" effort with a number of participants, and some incentives to populate the database.   (Disclaimer: My A1G Atlas First Generation website and my monthly Unofficial Micro-Trains Release Report are sources of information, but I'm not directly involved in the database-- I don't have the time.)  Here's the link:

http://www.trovestar.com/generic/group.php?Collection=4

Perhaps a "crowdsourced" approach to the Preserved Rolling Stock would work as well.   There is the additional complication for Preserved Rolling Stock in that the list is at least partially dynamic-- Steam Era Freight Cars and other items are bought, sold, moved and (unfortunately) destroyed.  

It took several years for the N Scale Database to get to where it is.  I don't hold any illusions as to how long it would take to create such an online list for Preserved Rolling Stock.

George Irwin
Rochester NY
www.irwinsjournal.com