If you found a firearm and did not know who the owner is, then you would be advised to call the police and have them pick it up; they can find the owner.
It is best to call the police and have them pick up the gun. If you must move it (say, to make sure some child doesn't find it), use a napkin or a paper towel, place it in a plastic bag and take it to the police. It may have been used in a crime and you really do not want your prints on it.
You don't. That information is not available to the public. It MAY be available to police officers.
You cannot. There is not a national registration system for firearms. Hopefully, there never will be.
Tell a responsible grown up, and leave the gun RIGHT where you found it.
Find a competent gunsmith. Failing that, get the apppropirate owner's manual.
Any of the on line auction sites, gun shop, gun show, Shotgun News.
check with your state police
You may be asking about Numrich Gun Parts Corp.They may be found on the web.
Gun auctions can be found from many different resources. Online, some of the best resources for finding gun auctions include the websites GunBroker and Calguns.
Photocopies can be found on ebay.
I have found Stevens manuals on the Numrich gun parts web site E-parts.com
Follow the instructions in the owner's manual. If you don't have one, request one from the maker. If they don't have a web site or don't exist, find a gun smith.
Follow the instructions in the owner's manual. If you don't have one, find a gun smith.