Although my research has been related to my Triumph Trophy, it is directly applicable to BMWs as well.
I have been needing a male plug to match up with the OEM power port on the Turnip. Some Hinckley folks have said a BMW-style plug will fit. My problem is that I've never actually seen a BMW-style power plug. Triumph RAT to the rescue.
http://www.triumphrat.net/Rather than over pay for a plug, I discovered John Deere Tractor dealers have both the male and female "BMW-style" components for a great price.
The male plug is Deere part #RE11340 for $7.30USD. The female socket is offered as part #AL25073 for $3.80USD or a more stout female

as part #MG82002966.
Also, the Powerlet folks offer BMW-style components.
http://www.powerlet.com/product/basic-plug/275Hope this is helpful.
Monte