I vaguely recall seeing something a while back, but honestly cannot recall details now.
That being said...I've made my own in the past. Used to have an Adaptto controller on my Fighter that would accept a variable voltage input for regen. So I bought some variable voltage hall sensors, stuck them to my brakes and put magnets on the levers. It took a bit of finesse but eventually I was able to tune it so that there was no perceivable point at which it went from regen to physical brakes.
I loved it and do miss it (I sold that bike about a year ago) and wish my other bikes that have regen also had it.
That being said, what I do instead now is using the CA V3 I program in a ramp up rate for regen and use levers with switches, then set the regen to a moderate level. Seems to be good enough and still captures a decent amount of energy and makes brake pads last plenty long.
Cheers