You could try USA based Forum members kharris and ljerr2 for a Cutts Compensator. Both can be contacted via Private Message
Mulberry Field produce a range of "Real-Look" cartridges in both cap-firing and Dummy types. I'm not sure if their .45 ACP Real Look cartridge will cycle and fire in the MGC Thompson as I think they're a different size to the standard cartridge.
If you just need display only cartridges, inert real ammunition is considerably less expensive than Mulberry Dummy rounds
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Cerwyn
Hobby collector of Replica model guns and Militaria.
also member of Living History Reenactment Groups.