Hi Gnasher...
I've got Mcguard wheel locks, they seem to be the best, about £30 from an Ebay seller.
https://www.ebay.co.uk/usr/diycarservicepartsThe specs are; M14 x 1.5mm and then whatever thread length you want. The standard length for Parker alloys is 25mm. And yes cone seat.
Funnily enough I've had to order two sets
one set at 35mm length as this what my new wheels need, and also another set at 45mm because I've just ordered a pair of 11mm Forge spacers for the rear wheels.
So what I might do is put two locking bolts on each wheel for even extra security