My friend runs a company called Foam Brain Games. They recently started doing bulk stickers are are fantastic to work with. Right now its quote only but he said they moving to general pricing. They also do enamel pins. www.foambrain.com

Foam Brain Games - Plastic and Metal RPG Dice, Enamel Pins, and more!

Make your next game night a Critical Hit with a set of beautiful metal dice, plastic dice and gaming accessories or wear one of our custom enamel pins from the DnD collection, Pride collection or Mons...

I've done the Gen Con Pin Bazaar and so I've had them make pins for me! I didn't know they did stickers too. (Although I do have some of their stickers from their booth at GAMA this year, come to think of it.) Very hard to comparison-shop without a published price list though :/