Its listed in Jimmy Macs excellent build thread somewhere as well as in a number of other threads here (original bits?).
I believe that it was from the Mini rally program.
I have been trying to work out what switch to use for my build as well but have not sorted out a solution to that yet.
I see there are a number of systems out there that will self-cancel an indicator. This is something that i was thinking about just this morning. Googled "GPS canceling turn signal" and got more than I was expecting. So it may be possible to get something that looks like the MK II flash to pass stalk, that also worked as an indicator/turn signal in the vertical plane.
I think other threads had suggested that a Volvo P1800 stalk was close in looks.