Where abouts in the Northeast are you bcharlton?  The BJ's in MA only carry the 8 oz bottles, not the mexican.  I can occasionally get it at Stop & Shop for a buck a bottle, but I think I may be wearing out my welcome there having them special order it....................
Same here in south-central PA - BJ's in York only carries 8oz HFCS sweetened Coke.  Both Sam's and Costco have the 12oz Mexican version near me.  
I also have Reading Draft about an hour north in Reading PA. 
http://www.readingdraft.com/Reading_Draft/Sodas.html  Been around since 1921, they brew their own root beer, sarsaparilla birch beer (blueberry, white and red), black cherry, grape and a few other flavors.  $10 a case in 12oz bottles.  I think it's 12 bottles to a case, can't quite recall.  Real friendly folks too - I make a trip there a couple times a year to stock up.  Makes a nice change of pace from Coke.  Different, because they don't 'flash carbonate', my wife thinks it tastes flat but there is carbonation - just much smaller bubbles than Coke/Pepsi.  They also sell by the keg and fountain bags.   (heh, and no - I don't work there)
Jim