cruise-o matic transmission needed

Hi everyone,
I'm a new member here and as I wrote in my introductory post I was lucky to find a '58 Skyliner in Germany on my business stay there. The car is great except for lack of transmission. I'm thinking of getting a rebuilt one or one that will have potential for a perfect match. The previous owner gave up on fixing the original transmission, lost it and was thinking about converting the system to manual.
Could anyone guide me through this search or point out other options ?
As I'm not familiar with the topic I would really appreciate the help.
Best,
Robert