For all the years I rode a Harley, I carried in a leather Helicopter Pilot Holster. It rode on the upper left chest, not buried like a shoulder holster rig. Probably the most dangerous times for the rider is when stopped at a traffic light or stopped and still on the bike at a gas station. By unzipping the riding jacket just enough to access the gun, you have an easy solution to what could be a difficult problem.
If memory serves me, I think I bought that holster from Cheaper Than Dirt when they used to be cheaper than dirt.