Couple of things I've found which seem promising:
https://neuromixer.com/products/avmixer-pro (formerly iMixHD)
Spark D-Fuser, a laptop fader which seems to have made a small production run of product and then stopped.
I believe these work by controlling the 1T-C2-750 made by tvONE. A little pricey ~$1000 but at least an option.
Also, V-1HD by Roland.