Thanks for that advice guys. That might be why my initial email was unanswered.

About 25+ years ago, when I was holidaying in England, one of the highlights was visiting Holland & Holland several times, (also Rowland Ward books which were then downstairs), and I got on very well with the staff there. I remember purchasing some silver-plated 12 gauge snap caps for a friend and the salesman told me, "one day Sir we'll build a gun around those for you".

Seems like I might just have to go back and search these records myself - but only if you insist, twist my arm and all that. But in the first instance, since I live on the other side of the world, I'll try contacting them by phone, (a bit cheaper than a flight ticket), and see what they say.
Anything of interest I'll report back.