gun show, gun shop
Find someone who reloads shotgun shells. They will relieve you of your inventory.
Remington
18, the same as every other state.
Most commercially available shotgun shells come in boxes of 25.
Air soft shotgun shells are the size of 12 gauge shotgun shells.
No
You can use nothing but 410 shells in a 410 shotgun.
This is a Browning Auto-5 Shotgun, 16 guage made in 1950. It is chambered for 2 3/4" 16 ga shells
You will have to do internet searches to find out. I do not know what "cheap" means to you.
Look in the yellow pages under "gunsmiths". In my opinion, the firing pins should probably remain missing on this old shotgun. It was not built for modern ammunition and may not be safe. If you intend to fire it, get a qualified gunsmith's approval and use only the proper shells.
NO
Shot and Slug