It sounds like you want to collect stamps topically.
I imagine you could find suitable stamps from a variety of sites. eBay
could work, as well as Hipstamp. You might even find some people who sell stamps in that topic. I think there are some companies that make catalogues of all the stamps a certain topic. That way you know what is out there, and what you don't have. Who knows? Maybe they made a catalogue for stamps in your topical area...