If your rifle is a single shot rolling block type rifle, it was probably made by the J. Stevens Arms & Tool Company. These were made for hardware stores under the Marvel brand, and PROBABLY dates to the early 1900s. Not a great deal of information out there.
Can't be answered wihtout the serial number, even then, it will depend on if data has been published.
Without a serial number, there is no way to answer.
You need a gunsmith.
Start here: http://www.e-gunparts.com/model.asp?idDept=127
Savage would be a good place to start. E-gunparts.com might have one also.
I would contact Walther directly and ask for a parts drawing. See the link below
10-100 USD or so
US Patent Office
No
A Winchester model 1904 single shot .22cal rifle is valued between 90-350 dollars based on the rifle having between 10%-90% of its original finish remaining.
If you know who made it, and they are still in business, probably.