Usa
Mr George Hoenig
http://www.finefirearms.com/hoenig.html

Belgium
Liege Arms with Jaques Maillearo(spelling of his last name might be off...)
There's another more recent company in Belgium but the name escapes me right now.

Old names not in use right now:
J.Bourne, there should be a few old double's about in Africa, if memory serves me right made quite a few .600 double's (that's what the internet gunclub once told me, down right now to check)

Army&Navy
W&C Scott

Arnold