For your hitch you can go to any of those 2 web sites and look for the distributors in your area.

http://www.bageco.com/
http://www.hiddenhitch.com/Home/

As far putting Hobie on the top of your car I see no problem if you can come up with some innovative way of attaching it to the roof of your car. But watch out for the windy days and your driving speed. You do not want to collect pieces of your boat from the road.

Just my 2 cents.

Kris