Here is a nice selection of 18500 batteries from a reputable dealer.
Batteries - 18500 Batteries - IMRbatteries.com
Thanks Dan! I like that site a lot. What's interesting is that on their Terms and Conditions page they have this disclaimer:
BEFORE PURCHASE YOU MUST AGREE TO THE FOLLOWING:
I have read the warnings on the product page(s) and clearly understand the potential dangers of using lithium ion batteries. I understand that lithium ion batteries are designed and intended to be used within SYSTEM INTEGRATIONS OR BATTERY PACKS ONLY AND NOT E-CIGARETTES/VAPORIZERS. I will NOT USE the products purchased from IMR Batteries with or for E-CIGARETTES/VAPORIZERS.