worn out shocks will cause cupping. Did you replace the shocks yet? If not, no matter how many alignments, new tires you get, they will cup again, until you install new shocks up front.

http://www.procarcare.com/includes/content/resourcecenter/encyclopedia/ch25/25readtirewear.html

 

another possability is bad wheel bearings but that is a another longshot that would have shown itself by now.

 

Fond another shop. There are many other possabilites but not usual, but all four tires out of alignment etc is not making sense.