I know a place to buy them in bulk in Southern Ontario (not sure of your location), but they are from a dehydrated raw treat place, so probably not cheap compared to Petsmart. They buy locally, so none of that stuff from China with who knows what in it.
They often have specials where they put a large box of various chew treats on sale. It's expensive though, but a better way to buy in bulk of a high quality product. They are also very accommodating, so if you wanted a giant box of them, they might be able to work something out for you.
You might try beef tendons (I find these last a bit longer...I mean maybe another minute, not hours. lol), pig ears etc as well (I get them the same place), for variety.