Many bicycle shops carry roof racks of the kind you describe. Typical brands are like the ones found at
http://www.thuleracks.com/thule/default.asp?flash=true&height=600
or
http://www.yakima.com/index.html

__________________
John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E