Chronos has them for 8 quid plus shipping, called MT3 socket. Link here **LINK**
I've been through the same thing before, inexplicably they are more expensive than the equivalent tapered adaptor. Maybe not used as much so lower volume = higher price?
Course, if you have a capstan lathe, you could crank a few dozen out yourself one afternoon.
Edited By Hopper on 02/01/2018 08:11:37