I live in RI and work in MA and only qualify for 6 weeks of maternity leave. Am I able to qualify for disabilty benefits during the time that I will be on leave?

As you do not WORK in Rhode Island, the employer probably is not deducting TDI deductions from your pay (and they don't have to, because you work in MA). You can contact the agency, but I wouldn't be optimistic.

The possibility exists that your employer may have an STD policy that will cover you regardless of state - many, but not all, MA employers do (it is not required by law but in my experience in this state, is common). You will need to ask your employer about that.