If they do not know about it, ask them for the wholesaler's name so that you can call them. This is the size you need. There is presently considerable confusion about how well sprays work against bears. The new viewpoint by some biologists is that sprays work well against grizzlies but not very well against black bears. There are some important principles being overlooked by these people.
Habituated bears respond differently to sprays than wild attacking bears.
Habituated bears often move off a short distance when sprayed, then return quickly. But there's more to the picture than this. Under these circumstances, sprays are often ineffective. Second is the attacking black bear in a defensive-aggressive behavioural mode. These are usually sows defending cubs, but there are few accounts in this category.