Buying Shoes for the Twins

Why is it that whenever we are looking to buy shoes for the twins at the mall there is always Limited availability in their stocks. Last night we went there to buy them each a pair of sneakers for school. We've been through a lot of shops, but we never found a design with 2 pairs of the same size. Buying two different shoes is not a good idea because no matter how much we explain to them that they share or switch, they always end up fighting. Maybe next time, when I see something and there are sizes available, I should grab them before someone else does.