The 300mm lens arrived today and it is Exakta bayonet mount as I suspected and it fits perfectly on my Exakta VX. The lens has the Exakta "outrigger" shutter release that also controls the automatic diaphragm. This does not answer the question about the possible existence of an Edixa bayonet mount camera, but the lens is exactly what I was hoping for.

By the way I found the picture of the Edixa with Exakta mount: www.geocities.com/Vienna/1244/ebayb4.html if anyone is interested.