Follow the instructions in the owner's manual. If you don't have one, you can request one from Remington on their web site.
Send me your email & I'll send you a scan of the manual. If you want to purchase an original manual you can try eBay or gunbroker.com but most of those are just copies of an original.
The stock for this model gun can be found at cabella's
You need the services of a good gunsmith.
The RemingtonModel 121 fieldmaster was introduce in 1936 and discontinued in 1954
The Remington 22 special (used in model 12, 121, etc) is the same as a 22 WRF Occasionally Winchester or CCI will make a run of ammo but Remington doesn't anymore. Your have to search gun shows if you want to find some.
how to change the mazda 121 gearbox
All 121's are date code, see related links for the table/information for looking it up.
The serial number of Remington rifles will not give you the date of manufacture. The two or three letter code stamped on the base of the barrel will tell the year and usually also the month of manufacture. On a Remington 121 this letter code OS usually on the left side of the barrel right next to the front of the action. I have a 121 with the letter code "OF". This indicates that my gun was made in July of 1937.
You might try the date system on Remington's web site here... http://www.remingtonsociety.com/questions/BLACKPOWDERX.htm ....and possibly find your answer.
Model R-12
Check the date code on the barrel. See related links for information on the Remington Society of America.