Unsure of your term "unusable rifles". At one time, rifles that were worn or unsafe for use had the firing pins removed, barrels plugged, and were designated as "drill rifles"- used to practice the manual of arms. Due to legal restraints, this is rarely done now. In the US, the Dept of Civilian Marksmanship has a few Drill Rifles for sale. Band supply companies also sell dummy rifles- used for Marching Bands, they look something like a rifle, but are not firearms, not capable of shooting, etc.
This is a matter of opinion and cannot be answered.
there is you just have to learn how and start a company that does it
Daisy makes several different model Air rifles each one has a different price. The Red Ryder usually sells for $39 here in California
smith and weeson sells pistols but remington only shot guns and rifles
Accuracy International sells a variety of sniper rifles as well as gun accessory. For a full list of all of their rifles you can visit the official Accuracy International website.
None. Weatherby sells firearms. You will have to contact them or the latest BATFE figures to find out.
Gun shops, gun shows, pawn shops, estate sales, garage sales, on line auctions.
Cabela's sells some double barrel muzzle loading rifles. Pedersoli sells some double barrel muzzle loading pistols. You could also go to GunsAmerica.
Silvermane.com sells two types, one is with a wooden handle, the other is with a metalic look.
Marlin sells parts for these rifles as does Numrich. Marlin at - www.marlinfirearms.com Numrich at - http://www.e-gunparts.com/model.asp?idDept=158
American company Kimber Manufacturing creates, produces, and sells small guns such Solo and M1911 rifles and pistols.
Dicks sells air guns and rifles differently in each state. As an example they will not sell any air guns / rifles or bow & arrows in California. In other states they may sell a full line of BB guns.