If you're a bike nerd and don't know about Bikepedia, you should. It's a freely accessible online database of bikes and bike parts.
The database is a product of Bike A Log, which creates the electronic database for use by bike shops so they can easily find parts and know where to order them from. Bike A Log also provides bike shop software for product comparisons, a wheelbuilding calculator, and other gizmos.
The Bikepedia bike catalog goes back to 1993 with full specs on several bike brands. A bike shop should help you find oddball and unique parts, but if they're less than helpful you can try browsing on Bikepedia and then you can point out a specific manufacturer part number for the shop to look up in their distributor catalogs. I like looking at Bikepedia for one-stop access to bike and parts specs when I'm doing research.