(Under construction/I am still learning about merchandise outside Japan!)
The following guide is a list of officially licensed Pokémon merchandisers and/or retailers servicing the United States:
Pokémon Center Online
Nintendo World NYC
Loungefly
Wicked Cool Toys
Think Geek
Build-a-Bear
Hot Topic
Gamestop (& Think Geek stores)
FYE
Spencer’s Gifts
Target
Walmart