A big problem with stocking snap caps is the sheer variety of calibres available. The A-Zoom line is something like 250+ different cartridges, in theory; at give or take twenty bucks a package let's imagine the wholesale is $10, that's a lot of money tied up in mostly slow-moving stuff (that takes up a lot of space relatively). Any store should have 9mm and 12ga. until they sell out, but after that it becomes a guessing game even in common calibres like .308 or .45ACP, or even .22LR where the functions of dummy round and snap cap are usually performed by two separate items. 7,62x54R is a pretty big round in our market so you'd think everybody keeps 'em, but most stores are missing many very common hunting calibres like .270 so that's just the reality.
For site sponsors, I suggest searching the ones that lean more heavily to Red/surplus rifles, such as TradeEx, Westrifle, Frontier, Marstar… I have added dummies to any order when and where I found them, including from Wanstalls and Epps and anywhere. Chain stores like Cabela's, Bass Pro, Wholesale, should be able to transfer stock in from another location (or the warehouse on their next order), and even Canadian Tire out where I am has them.
Otherwise it's eBay and Amazon, the fall-backs for common firearms accessories like this. I have like two dozen different snaps, for any calibre I've owned, and have found the best price and selection from a seller on eBay who should be all over a search for A-Zoom. Note that theoretically dummy cartridges are Non-Mailable Matter as per Canada Post, and *could* cause panic if they show up on an X-rayed parcel. But honestly I've had them shipped, within Canada and across the border, from stores large and small or individuals, and it's never been a problem.