Have you tried calling Tire Rack. They are aimed at selling on the internet. but they do have knowledgeable people that answer the phone. It appears that you are in a position to mount your own.
http://www.tirerack.com/content/tirerack/desktop/en/homepage.html?s_kwcid=AL!3756!3!78748013533!e!!g!!tire%20rack&ef_id=VcjXWwAAANiT5Czp:20150810165451:s
