Sounds like a commission to me, or buy a new or estate prince and have the stem replaced. You might find one, but I feel it might take a lot of research. Is it amber you want or an acrylic facsimile.
I hate to do this because of all of the Peterson quality control issues, but Peterson has a line of pipes, the Rosslare and Rosslare Classic, with amber stems. Maybe you will be one of the fortunate ones.