Where to buy shells for vintage shotguns

Got a couple shotguns in a trade. This one is a 100+ year old Hopkins and Allen 16ga. Looking for someplace local to buy 2 1/2" shells made for vintage guns

Found some online, polywad vintages, but four box minimum and twenty bucks in shipping

....

I can't see your photos so I'm answering blind and may be way off, but I've seen some of the cowboy reenactment/show shooters reload brass cases. So, maybe you'll have to try to figure out what specs those guns are capable of then start custom loading them. Sorry if that's not much help, but maybe there is a cowboy shooter forum where you could find some help?

Found another online source

http://www.rstshells.com/store/default.aspx