Just got my new 2008-2013 HD Sportster voltage regulator to replace the original broken voltage regulator on my 2009 Buell XB12 Scg. And it works! It is two-three times cheaper than original Buell VR and it is easy to find. I bought mine on Amazon. The plugs fit like gloves. The only thing you have to do is to build a bracket to attach it to the frame (the mounting holes are in another places) and extend the wires (the HD Sportster VR wires are shorter than the original 2008-2010 Buell VR wires).
Will see how it will perform in the future.