I saw them advertised by somebody in a proper ad in the latest PF or FF, can't remember which, has green german cossie on the front cover.
It would be a lot simpler just to buy a trigger wheel, then just drill four small 4mm holes, tap them and screw on the wheel, even with a bit of maching you are looking at well under £50, and thw wheel will never break bits off, or corode(SS), an dif you ever went to another aftermarket ecu, you have no problem simply swapping cheaply available trigger wheel.
You can also use a dial gauge to line up trigger 100% spot on too.
The (NEW)ones I saw advertised though were about £135 from memory, think it was woodford, but can't swear to it.
tabetha