Seeking design help for accessible home

We are moving to a home that will better suit my son, a wheelchair user. Ideally, we'll find something already adapted, but if we don't, we'll need to convert the bathroom, maybe doorways, and maybe something in the kitchen to suit him. I'd like to get advice from a knowledgeable designer before we buy the wrong house. How can I find the right person in my area? Is there a site that lists designers who are accessibility experts?