Steve & Yogi:
You are very correct on the usefulness of both the 12-bore and the 9.3x74 cartridges, and the desirability of a drilling so-chambered.
This combination is historically rare in my experience, because you end up with either a 9 lb shotgun or a 7 1/2 lb 9.3x74, neither of which is ideal for shooting. Something in between will always be a compromise. I believe this is why the 9.3x72 was usually chosen as a medium-bore chambering for the rifle barrel, as it is still relatively comfortable to shoot in the lighter weights needed for a lively shotgun.
Of course, modern makers will probably build whatever is ordered within reason, but when tossing cash at a brand-new drilling in the suggested combination, serious thought should be given to the desired weight. A heavy shotgun may be OK for fowling, but is a real handicap when walking-up game.
If I lived in the US, I would talk directly with the guys at Heym USA, but any of the three makers listed produce marvellous products for the price IMHO.
