Travel insurances are "one offs" for special occasions and hence people buy them rarely, for a limited amount of time and don't research them very well. The insurance industry often takes advantage of this and many policies are insanely complicated with lots and lots of exclusions and limitation to coverage. If you want to find out whether a specific insurance covers a specific issue, you need to be prepared to spend a lot of time researching this carefully.
Disability is a complex topic. Every country has it's own set of laws that kicks in to cover a disability incident and it depends often on the cause (medical or accident) and time frame (short term, long term, permanent). This being said, there is relatively inexpensive "accident" insurance available that pays cash depending on type and severity of the disability. They only cover accidents, not medical. You can easily research through Google.
Keep in mind that Insurance is in the business of making money for the Insurance, so on average every premium is higher than the risk it covers. I would recommend to carefully research your existing insurances and local laws to determine what coverage and options you already have. Then identify any gaps you are not comfortable with and then research options to specifically cover this gap.