Bret,

Your options would appear to be:

Chapuis www.doubleguns.com
Krieghoff http://www.krieghoff.com/
Merkel http://www.gsifirearms.com/gsif/merch.asp
Searcy www.searcyent.com
Sig Blaser S2 www.sigarms.com
Off-name vintage guns in 450-400 if you get lucky www.champlinarms.com

I would avoid the Blaser because it's more of a gadget than a rifle.

Austrian .375 HH at champlin's for $8700:

Austrian .458 Win Mag at Champlins for $8400

Jeffery 450/400 for $10k: