It's not at all difficult to make one if you access to some basic metalworking machinery.
Having read mixed reports on the durability of the commercial items which appear to be stamped from soft aluminium I elected to make my own from a bit of 10mm mild steel.
Small hole up the centre, machine away third of that diameter, silver solder in a bit scrap steel to form the flat, machine the outside diameter to size to fit the recess where the pilot screw sits, Knurl the other end to get a grip and put a nice finish on to look good and Bobs your uncle.
Of course it helps if you have a lathe and a miling machine and some welding/brazing gear.

It's also my other hobby outside of motorbikes.