I have used this resource in the past for my University students:

https://www.cryptomuseum.com/crypto/enigma/hist.htm

They are based in the Netherlands (Holland).

Paul Reuvers & Marc Simons have pulled together a pretty comprehensive set of resources. You should be even be able to connect with other researchers on the subject through their specific link:

https://www.cryptomuseum.com/contact/index.htm

Hope this is helpful. Good luck with your own research efforts.

Regards, Dr. C