Goex sells 12 ga in a few shot sizes, you can get them from powder inc and Midway USA both can be found on the internet I think 10X ammunition also sells them.
18, the same as every other state.
No you will not. But if you are a regular customer maybe they will give you a discount
Fiochi
Ballistic Products , 888~273~5623
Matters on the clip size that the shotgun comes with (or that you buy) it can be anywhere through 6 shells to 12.
You cannot buy different sized shotgun magazines. However, I suggest getting a shotgun that takes airsoft shotgun shells. It will expand your options of bullet capacity.
1400.00
Most commercially available shotgun shells come in boxes of 25.
Air soft shotgun shells are the size of 12 gauge shotgun shells.
Google a company called Polywad. I have bought shells from them and was satisfied with their product.
I believe this gun is an 1872 issue
Find someone who reloads shotgun shells. They will relieve you of your inventory.