YORF has an interesting thread on rocket motor collecting. I'm a little jealous. My collection, if you can call it that, includes a mere three vintage/OOP motors: an early AeroTech G10, an early G125, and an Apogee B2. My number one interest in old motors is the old Estes B14s. I want enough that I won't feel bad about burning some :) I'd also like some Silver Streaks. However, I'm not really inclined at trying to pick them up at auction, so the real chances of getting any is slim.
Another post provided this link to a Czech site about motors from that quadrant of the world.