Several. Impossible to answer without more information.
You would need more than parts- you would need a tool & die maker's machine shop and the knowledge to operate end mills and lathes. The bolt action has an entirely different design than a semi or full auto.
Pull pump action back. screw the knurled part at end of stock to loosen it. Remove barrel. Turn knurled part all the way off and plug and spring should come out. Replace spring and replace knurled part. Replace barrel and you're ready.
If by chance you mean a Moisin-Nagant 91/30, it was the standard rifle of the Russian military from WW I through the end of WWII. It is a bolt action rifle in caliber 7.62 x 54R.
There were 2 rifles that were marked 31A. Both were bolt action 22s made by Mossberg- the model 40 and model 44. For both: Open the bolt, insure rifle is empty. With the safety OFF, bolt open, press trigger to the rear and hold it. The bolt will slide out of the back of the action. Turn rifle over, and unscrew the single large screw at the underside of the stock. This will release the barrel and action from the stock. The 40 uses a tube magazine- turn the end, slide the inner magazine tube out of the outer magazine tube. The 44 uses a box magazine- press and hold the magazine catch, and withdraw the magazine. At this point, you should STOP taking things apart. This is enough to clean and lubricate the rifle.
1984
Try your local gun smith or gun show.
K-65 my uncle brought me one from Germany at the end of WWII
First, make sure the rifle is unloaded. Then pull the bolt back to the end of it's travel. Inside the trigger guard, just fwd of the trigger is a relatively small button (bolt release) push it and remove your bolt. Reverse this for installation. Hope this helps.
Quite simple really. Wrap a dollar bill around the barrel at the muzzle end and slide it back toward the action. You should get no resistance as the bill passes between the stock and the barrel and it should slide easily all the way back to the action.
standard battle rifle of u.s soldiers in WWI was a 1903 Sprinfield bolt action rifle. As for machine guns the most commonly used was a variation of hiram maxims machine gun, but they did use the 1917 browning designed one towards the end of the war
The singleshot Stevens 15A and 15B .22 rifles are worth %50 to $150, depending on the condition. The higher-end price seems to keep them sitting around for quite a while.
Insure that the rifle is unloaded. The rifle must be cocked, so that the firing pin does not protrude from the bolt face. With the bolt closed, insert a wooden dowel that is close to the bore size into the muzzle, and slide down until it contacts the closed bolt. Mark the dowel at the muzzle, withdraw, and measure distance from mark to end of dowel. This is also the technique used for most other firearms. REVOLVERS are measured differently.