Taconic Arms in New York offered a full Titanium Mauser action more than 10 years ago. That was taken over by Stuart Satterlee when Taaconic got out of the firearms business to concentrate on aerospace components in Titanium. Right now, Armeria Concari in Europe also offer Titanium Mauser actions. Fanzoj are the latest addition to the list. However, while others offer the kurz style action in Ti, Fanzoj offer both the kurz as well as standard size actions in the material from what I understand.

Good hunting!