Hi Kerland
After reading an advertisement claiming real Stirling mags fit the MGC Model, I foolishly bought two and they won't go anywhere near the Modelgun.
You may, possibly, be able to use a real Follower and a much shortened spring from a real mag with some modification inside the one you have.
Your best option may be to contact Francky or Shazhib, they may be able to find you a genuine MGC Sterling mag.
There are 2 sources of custom made steel Sterling bolts, Modelguncollector.co.uk and Ken Harris.
It is worth checking Modelguncollector.co.uk regarding shipping PARTS overseas.
Ken has a bolt for sale on Gunbroker.com
Be aware too that you should only ever attempt to fire PFC Cap loaded cartridges in your MGC Sterling, don't even think about trying proper Blank Fire ammunition as one would destroy the gun and do you some serious harm too.
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Cerwyn
Hobby collector of Replica model guns and Militaria.
also member of Living History Reenactment Groups.