hoppdoc
I know that you can get a Krieghoff double in calibres from 500 Nitro, down to 7x65, including 20 ga shotgun bbls.

The Chapuis can be had in 470 and 12 Ga.
The Chapuis is the only modern made double that can be had in 12 ga as far as I know.

Heym can be had in multiple calibres as well.

2 doubles, a Chapuis in 470 and 12 ga. And another in 9,3x74R and 30-06[for an American hunter], or 7x65 [for a European hunter] would be a hard combo to beat. You can also get 20 ga bbls for the 9,3 Chapuis... I wish I had a set for mine.