Champion Sidecar in Huntington Beach; Legend and Escort modelsfits 750cc and over. We were looking at them for the 03 883 XLH, but triked out a Electra Glide for touring instead. We still have the Sporty and I am undecided as what to do with it.
Side cars are a different ride. If you are really condidering this, check out the info on some of the trike and side car threads. One rider lost a lower leg and taught himself, after doinga lot of resource reading.
There are also three wheel classes offered through EverGreen, MSF basic courses. They will get your through the 'gotta think different' parts of the skill set.