Doc, are you looking for general field use or suitable for under your tux? That will certainly make a difference as far as what I might suggest (I know how you doctors are, cocktail parties and formal events at The Club on weekends....)
EDIT: You know what, let me just toss a couple ideas to you.
Forum member "Robbt" has shoulder holsters among the dozens of holsters in his classified ad in the "miscellaneous" section right here.
Sportsman's Guide has some shoulder holsters on their site, too. sportsmansguide dot com.