Try a want ad or a gun show.
Try egunparts, on line auctions, gun shops, gun shows.
You can find it on e-gunparts.com
Egunparts has some.
Start here: http://www.e-gunparts.com/model.asp?idDept=127
Take it to a gunsmith and ask for help
http://www.e-gunparts.com/product.asp?chrProductSKU=PDF0546
Go to Numrich Gun Parts Corp.they should have what you seek.
http://www.e-gunparts.com/productschem.asp?chrMasterModel=0860z788
It all depends on the condition and model of the rifle. Daisy has made several versions of the Single Shot. The model "A" Single Shot, model "C No1", model "C No2" and the "Sentinel Single Shot". Most were made in the early 1900's. Can you Identify your model?
single shot 22
No such model. Winchester did not make a 'Model 1901 single shot .22 pump-action rifle.' They made a Model 1900, Model 1902 and Model 1904, which were all single-shot bolt-action rifles, and they made the Model 1890 and Model 1906 which were slide-action rifles but had tubular magazines. How exactly is your rifle marked? sales@countrygunsmith.net
The correct answer is Numrich gun parts. Or, just google Marlin A1 schematic and it will show you a list of parts that you can order and a complete schematic to view.