Other than the Blizzard gear store, where might I find a catalogue of official Diablo prints that have been created over the years? Or even better, where might I buy them? I looked on eBay but can’t tell what’s official and what’s just a screen print of something that I’m being overcharged for.
Check out the art section on the official diablo site to get an idea for what the official art looks like and what's been available. Other than posters sold in the blizzard store, you're probably not going to find much else. Diablo historically doesn't get much merchandise.
You might be better off getting high res art printed yourself.