Look for the nearest AMPM using this link http://find.mapmuse.com/brand/bp-amoco-arco-ampm
If you live outside North America, you can't find an AmPm near you or you don't want to stand up from your chair, you may opt to use eBay.com to buy the cups, here is a link:
Vanilla Warcraft
Burning Crusade
Wrath of the Lich King
Cataclysm