I get them at my LGS. They come in a duplex buckshotload with three #1 pellets and seven #4 pellets and a slug load. Cannt remenber velocity but they do kill up to 30 pound raccoons real fast. They also make a bird shot version that I have never used.
I imagine if you googled some ammo retailers you would find some online.
I imagine if you googled some ammo retailers you would find some online.