while technically you are not prevented from buying a policy on a marketplace it is more likely that it will duplicate rather than cover the gaps in your medicare policy. the marketplace is designed for people without insurance or people trying to replace their existing policy. there are no medicare supplemental policies on the marketplaces which sounds more like what you might want. about half of states require medicare supplemental insurers to offer medigap policies to those who are on medicare due to a disability. you can visit a state health assistance insurance program in your state which provides assistance for people with medicare. because of the federal government shutdown the best way to find a ship in your state is www. shiptalk. org.
if you have medicare because of disability can you still get a health insurance policy on the marketplace?