If you're in North America, there is now a wheeltop.us. Still shipped and serviced from China but legit 'local' factory store.
You might have a problem sourcing for that config though. AFAIK, the cable brake configuration is only available in the 'road' set and its RD only support 36t max sprocket. The GeX 'gravel' setup can go to 51t (or 40 something with the short cage) but appears to only hydraulic brakes.
So the question is whether you can buy the shifter/brake unit from the road kit and use it with the gravel RD. In THEORY I see no reason why it couldn't since the gravel shifters are really road shifter anyway. But it is possible that the combo is software locked. I'd ask Wheeltop directly what parts to get. They seem reasonably responsive to sales questions.