Does anyone know the procedure for getting a patient approved for a power wheelchair through Medicare?

thanks so much!

Since you said you wanted to get the chair through Medicare
https://www.medicare.gov/coverage/manual-wheelchairs-and-power-mobility-devices.html
Manual wheelchairs & power mobility devices
How often is it covered?
Medicare Part B (Medical Insurance) covers power-operated vehicles (scooters) and manual wheelchairs as durable medical equipment (DME) that your doctor prescribes for use in your home. You must have a face-to-face examination and a written prescription from a doctor or other treating provider before Medicare helps pay for a power wheelchair. Power wheelchairs are covered only when they're medically necessary.
Who's eligible?
All people with Part B are covered.
Your costs in Original Medicare
If your supplier accepts assignment, you pay 20% of the Medicare-approved amount, and the Part B deductible applies. Medicare pays for different kinds of DME in different ways. Depending on the type of equipment, you may need to rent the equipment, you may need to buy the equipment, or you may be able to choose whether to rent or buy the equipment.
Medicare will only cover your DME if your doctors and DME suppliers are enrolled in Medicare. Doctors and suppliers have to meet strict standards to enroll and stay enrolled in Medicare. If your doctors or suppliers aren’t enrolled, Medicare won’t pay the claims submitted by them.
It’s also important to ask your suppliers if they participate in Medicare before you get DME. If suppliers are participating suppliers, they must accept assignment. If suppliers are enrolled in Medicare but aren’t “participating,” they may choose not to accept assignment. If suppliers don't accept assignment, there’s no limit on the amount they can charge you.

Also, there are used ones out there. Guys will buy them cheap or get them free, fix them up a little and sell them at a fraction of the original costs. Check on line for your area.

Agree with Jeanne it has to be prescribed but don't expect it to be easy or fast. none of these expensive pieces of equipment are. Is there any chance that the family could afford to rent one?

I'm sure it needs to start with a doctor who "prescribes" it for him.