I got my AW IMR 18650's from
Lighthound, and while you're there, pick up one of
these little carriers - they're cheap, and will hold a spare 18650, a spare 6ml bottle, and a spare atty perfectly - an overnight kit for your Grand! They also, if I recall correctly, toss in a little freebie led keychain flashlight that just rocks - super bright, and lasts forever.
Edit: Don't be swayed by higher mah batteries out there - these are absolutely the best battery to use in a Grand - the discharge rate and chemical safety (instead of 'protected' which contains a chip that can fail, or 'unprotected' which can start a fire) make them the optimal battery for this application. Plus, the higher mah batteries are a little taller, and can hurt the Grand by bypassing its' spring safety.