Number of special clinics?

How many do you have per million to keep the number of disabled from rising?

That all depends on how many CEO corporations you have in your country.

Assuming zero.

The Special Clinics are sponsored by CEO Controlled Corporations. Therefore you are able to rehabilitate 40% of the number of workers you have in CEO Controlled Corporations. The maximum number of the disabled that can be rehabilitated is also limited to 50% of all disabled workers.

So, keep building clinics until you reach 40-50% of the number of workers in CEO corps.
Not evry country will be the same.
The same basically applies to "back to work schools"

As far as I can see, it works even without any CEO corporations in the country. The only difference is the cost and the efficiency (half).