Excerpt:
The stolen machine is one of the Enigmas used by the German military intelligence service - Abwehr. There probably are more than three of these machine left but they are extremely rare and I would not be astonished to find that only a handful remain in existence. The only other machine of this type we know about in a museum with public access is in the National Cryptologic Museum, at Fort Meade, MD, USA.
Annotation:
This is a clearinghouse of all things cryptology on the internet. This site could be useful to researchers in this area.