Do you ever have speciality conversion vans for wheelchairs?
There are companies that convert standard vans to accommidate wheelchairs. Are any of these ever listed on craig's list? These can be almost any make of car. They kneel and have a ramp that automatically folds down to let the wheelchairs enter easily. Some even are able to let the wheelchair replace the front seats of the vehicle with the wheelchair. Some can hold as many as 4 wheelchairs and still have a bench seat in the back for regular passengers. They have a safety lock system to lock the wheelchairs down that they don't roll around while on the road.
There might be, just hard to find. I just searched www.craigslist.com in my area and under search in "cars and trucks", in teh search string type in "Van wheelchair", it found 58, but not all are as big as what you want. Keep looking and you'll find something.
I have a relative that has a couple of vehicles that they've had modified. They live in KY - They used Superior Van and Mobility, and have multiple locations: Check out http://www.superiorvan.com/
You might try asking a local nursing home, emergency squad, or special needs school. They often use vehicles equipped for transporting people in wheelchairs. They could probably tell you where they buy from. Then you can contact the vehicle suppliers directly. HTH. -Jim