If it is a standard order item (like these 2-packs), almost any place is reliable.
It is just the exclusives that you have to watch for... if it is a Convention or a Medicom on-line exclusive (like the 2008 Box set, the Maul Bike set, etc), your chances of getting it at an etailer like BBTS, Toywiz, ActionHQ, etc are less than 1%.