Hi Henri..The only place I know has these is Russell Motors...though Draganfly might have them as well. I would think machining something up to blank the end of the bush would be the easier option for you...it is not really visible when the bike is assembled.
I'd take a look to see why the layshaft bush is off centre in its housing as well if I were you..Ian
Interesting you note that the bush is off center. Not by much so it seems, .40 mm. Might as well order another and see if it improves. It has the groove at 0900 hrs.