Mathis Instruments in the US.
http://www.mathis-instruments.com/
The are famous for the MI-250 which is sold by Mountain Instruments.
They have a Fork version MI-500F, MI-750F, MI-1000F etc. They could possibly make a custom one for you. But these are not cheap.
Each one has a GEQ version and a Fork version. The F signifies fork. The MI-500F is about 12000USD.
But then you have to add a Goto system, on the MI-250 you can use the Gemini system. But for these larger mounts it looks like you get the Bisque goto system, I assume this is similar to the Paramount goto system. The BISQUE TCS electronics are 4400USD. The dont list a price for it but do mention you can also get the Astrophysics GTO system.
Regards
Fahim