No, they don’t make them anymore. You can try buying a used control head for the ST4000+, but note that I. This early version, all of the electronics are in the control head.
I found a “new, old stock” ST6000 a few years back and upgraded my system. The ST6000 upgrades the system to have a separate CPU (brain box). If you could find a used ST6000, with the control head and course computer, that would be a good upgrade. The compass and wheel drive motor are essentially the same.
The current version (EV100) uses a separate course computer like the ST6000 and has an upgraded compass unit. So some rewiring will be required if you go this route.
Greg