Smallbore,

There is a place for such a rifle in the US. An English made and styled double at that price is not offered right now. Still, $25k is a lot of money, so your marketing will need to be effective.

9.3X74R is a must, more so than the .375 Flanged. The two are close enough that ammo availability tips the favor to the 9.3.

Other calibers, 450-400 3", .450 3 1/4, .470 and .500 would round out what would be most requested.

Look into the sales of the Robertson guns from Boss. If they were sucessfull, your efforts probably will be as well.