Where to find a device (winch?) to help an elderly person get in and out of bed by himself?

Call the doctor, who orders an OT assessment in the home. If Dad needs a "hoyer lift" to get out of bed, he is not going to do this by himself.

Bring in an occupational therapist. This professional will assess your Dad's needs and make recommendations for equipment. AND, the therapist will also show the patient how use the equipment.