When I was in MI this past summer a friend and I drove our asses down to Ohio to buy some 20x from a headshop there. What major city are you nearest to? If I recall correctly, there's a big chain of stores called Waterbeds 'N' Stuff around Columbus. It will cost you a bit more, but for us it was worth not having to stress over getting to the mailbox first- legal or not. Not to mention lots of places won't ship packages to PO boxes.