you have the M261 style. there is a place in the states, SARCO. they have/had spare mag inserts and some spare parts.
Oly Arms is also making a copy of the same system, but i am not 100% sure of compatibility. Black Dog Machine is making fullsize mags for these. no inserts needed. get the Black Dog mags. 28 rounds instead of 10. plus the plastic doesn't hurt your fingers as much while reloading.
if you haven't got a kit yet, just get a Ciener kit. there are OEM and Black Dog full size mags, aftermarket upper that do away with the adapter, aftermarket spring kit and aftermarket replacement parts.
alot of people say JAC is a douche, but there are dealers that sell his stuff that are easy to deal with.