Step 1:
Don't be poor.
Step 2:
Be rich.
Step 3:
Offer lots of money for them in open, by PM, and on eBay. If you go the PM route, make sure to PM everyone who had ever posted pictures of them, but especially seconds after they post pics.
Step 4:
Own lots of Clacks and Bros.
Step 5 (optional):
Get lucky in sales.
Hope my definitive guide helps some of you find your dream caps.