I see a lot of "I'd like a keycap with my username" threads.
These end up with one guy taking 15, and maybe a few other people in.
Why not try to make a pool of those individual orders:
If you get 15 people all who want one of a different design, you can make 15 units of each, and send one of each to every participant. Then nobody HAS to buy 15 to meet the quota, and everyone gets an assortment.