Gun show, gun shop, on line auciton, magazines, catalogs, pawn shop, want ad, garage sale, estate sale.
No, mechanical guns are operated by a trigger (i.e. tippmanns, spyders). You can however buy a rapid firing crank from some paintball and firearms manufacturers.
no
Which company?
In modern firearms, the trigger allows the firing pin to sharply tap the primer on the cartridge...which, in short, fires the gun. The actual mechanics of the trigger mechanism vary for every weapon.
upper reciever, lower reciever, trigger mechanism
There are on-line forums devoted to specific firearms, including the Mosin Nagant- they would be a good starting point. The link below will take you to one such forum.
A device which sets a machine in motion, usually rapidly.
Contact BATFE.
No
Some you can.
No
Pawnshop