I'm pretty sure they are available, if you contact a disability employment service, they may be able to point you in the right direction.
I tried several different types of keyboards, including split keyboards, tracker balls instead of a mouse etc - for me none of them were any good. There was a company that provided accessories for office workers with a disability, that I visited. (very interesting)
I now use a keyboard with a touchpad and NO MOUSE. My arm is permanently impaired from overuse of a mouse, but this keyboard has been great. The brand I have is Addesso, I live in Australia, but I'm sure there are others out there. It wasn't very expensive either!!!
I don't know if this keyboard would help your particular problems, but not having a mouse on a standard keyboard is great.
I wish you well in your search, and improvement in your problems.
They say life is a bowl of cherries........... we just have to learn how to spit out the pips!