I remember doing a 'Duke of Cornwall'... (I grew up in Cornwall)...
A suggested modification:
If the Duke of Cornwall has RNAS Culdrose then he probably has this firm
http://www.helstongunsmiths.com/ (it's literally just down the road)
I'd assume that most of the stock was requisitioned early in the Twilight War - but some of the odder stuff (Mauser rifles?) might have been left and some of the personnel may still be available to repair the deactivated weapons
Seriously... check out the de-activated weapons on the site, I can imagine the 'Duke' carrying something like the gold-plated sterling SMG on formal occasions