Try your local gunsmith's shop. He can probably find one that can be fitted to it. Or carry it to a lot of gunshows and dig through all the dealers' bins of miscellaneous parts.
The 7G prefix to your serial number indicates that your Browning light weight 12 gauge auto-5 shotgun was made in the year 1967.The value will be between 340-450 dollars for a plain barreled model,and 415-630 dollars for a vent rib barreled model.This is assuming that your shotgun has between 60%-90% of its original finish remaining and a good bore.
Long barreled shotgun
Gun shop, gun show, Shotgun News, Gun List
sawed-off double barreled 12 gauge Remington shotgun.
Short barreled shotgun is actually a legal term- it means a shotgun that has barrels less than 18 inches, or an overall length of less than 26". To my knowledge, H&A did NOT make a short barreled shotgun. Information is thin- they went out of business about 1914-1916, but all listings I have seen are for 28 inch barrels.
Parker 12 ga muzzleloader
50-100 or so
No, according to RCW 9.41.190: "It is unlawful for any person to manufacture, own, buy, sell, loan, furnish, transport, or have in possession or under control, any machine gun, short-barreled shotgun, or short-barreled rifle; or any part designed and intended solely and exclusively for use in a machine gun, short-barreled shotgun, or short-barreled rifle, or in converting a weapon into a machine gun, short-barreled shotgun, or short-barreled rifle; or to assemble or repair any machine gun, short-barreled shotgun, or short-barreled rifle." You can thank the assault weapons ban for this. There are exceptions though: http://apps.leg.wa.gov/RCW/default.aspx?cite=9.41.190
A short barreled shotgun is not necessarily "more lethal" than a long barreled shotgun. However, it is more readily concealable, and has lost most of its usefulness as a sporting (hunting) weapon.
'Granny' used a double-barreled , 12-gauge shotgun .
No.
Stevens Arms made the Ranger shotgun for Sears & Roebuck. Production ended about 1930.