I might spend a week prototyping something.. perhaps stabilised using very small high speed brushless motors for gyro effect, with some flexible/springy elements. The motors cost $5 or so each online. The design would be open source.

I'm not familiar with the disability however, I'm not sure which axises of motion need to be stabilised.

Get in touch if you are interested, my email is in my profile.

EDIT: What about EMS pads on the major arm muscles, accelerometer/gyro chip on the pack of the palm, and pipe it into a machine learning system that figures out the correct stimulation for stability? Is that a thing?