Brett

I'm going to move this thread to the Double Rifle forum tommorrow.

For 10G you will have a number of choices. For 5G or less you may find medium bores to about 9.3mm but less likely to find a larger bore.

Chapuis, Merkel and Searcy are three that are in the USA that you should consider in the 7G to 10G price range. Krieghoff and Heym may be more than 10G. Probably other makers may fit your price too, maybe Blaser if you like them.