There is always the solution of grinding up regular-sized crackers, mixing them into a paste or something, then pouring that into a mold or pan. Or, you know, enlargement magic. Because the simplest solution is usually the best.
I think there's a book on it in the Canterlot Royal Library. Two rooms down from the time travel, first stack on the left, top shelf, somewhere in the middle. Next to it is a large coinpurse. Have fun shopping for those jeans!