BMW makes one, about $1200 installed at the dealer.

I did setup (see this post 2011 Tow Hitch - Page 6 - bimmerfest - BMW Forums)

$184.00
Draw-Tite Class III Hitch (Part Number: 75600)
got from
Trailer Hitches, Hitch Accessories, Hitch Wiring

Tow Ready Wiring part number 119176

Upgraded Modulite Circuit Protected Vehicle Wiring Harness with 4 Pole Trailer Connector Tow Ready Wiring 119176

Mount Bracket

Mounting Bracket 4-Pole Flat Tow Ready Accessories and Parts 18144


Total cost was about $250 shipped or a bit less - about 4 hours to install.