Mahely is a previous trademark Giachetti Gonzales & Cia in Buenos Aires.
The rifle was not regularly exported and you may have trouble locating parts on your own.
I suggest you do a search on the web for "Airgun Repair" and locate someone near you to repair the rifle.
Not a lot of information on these guns, All references I can find show them in Argentina- they seem to be utility grade .22 LR semiauto firearms, similar to the older Mossberg 22s in their design. Numrich has a very limited number of parts available. For a shooter grade .22 semi, value would probably run $100-$150.
Numrich gun parts
Try egunparts.com
You can find a lock for a Mahely Carabina auto caliber .22 part 115277, model M21 117070 on eBay. You may also be able to find this piece through avid gun collectors online or at auctions.
Which model??
you can find parts for your Stevens at bob`s gun parts .com
We have parts for that model. gunshop@nctv.com
Check with a gunsmith, or find the model number of your rifle, and check on line parts supply houses, like gunpartscorp.com
Try Nurmich Arms
Numrich Arms is a good source for gun parts.
Go to Numrich Gun Parts Corp.
The National Rifle Association does not have a specific "Grand Senior" classification. However, they do have various senior age categories for competitive shooting events, such as Senior (60+), Senior-Veteran (70+), and Super Senior (80+). These classifications are based on the competitor's age and are used to ensure fair competition among participants.