Mitchell was only a distributer of the stainless Lugers.  After Mitchell, Stoeger took over distributership.  At the point Stoeger took over they changed to a non-standard magazine.  Now they are sold direct from the factory and shipped to your local dealer for the transfer.
Go to:  
http://www.lugerforum.com/Sign up and you will find a good deal of information on these.  (They are still in production.)  Unfortunately it's a member only forum due to past problems with people bringing their flame throwers to the party.
The manufacturer:
Orimar Firearms Manufacturing, Inc. -  R.E. Romo, Orimar Corp, PO box 8767, Houston,TX 77249-8767, (713) 305-8540 
Current Reproduction Stainless Steel Lugers  (Former producer of Mitchell, Stoeger and AIMCO Stainless Steel Lugers)