Who prescribes new bed?

The motor which raises and lowers my 34 year old Borg Warner (no longer in business) bed has apparently died (the motor that raises and lowers the back or knees is fine.) Who should prescribe a new bed, and who would supply it? I presume Medicare would pay for it, as I've never gotten a bed through them.

I hope this is simpler than getting the low air loss, lateral rotation mattress I need, but have not been able to get.

Thanks for the help.

Who prescribes new bed?