Why do you have to bother with new? Just do what we'd do.......... Get another out of the tray - any one will do - and fit that to the rifle. Test for feed and functioning with drill rounds. Get it sorted, then bar out the old number(s) and send the rifle out, back to the Armoury
At the big workshops we'd wait until there were 25 or 30 or so defective magazines with worn back straps or dents and start a big repair programme. Cut back the worn part of the back strap, silver solder new, take out dents on a mandrill, police out lightly punched numbers then send through the phosphating plant. They''d all come out not exactly new, but rebuilt for a further 30 years of life. I'll tell you this........ We didn't bin very much!