Thanks for your thoughts here Nick and the link, that is a handy one for sure.
If I can't find one, I'll likely buy one in the same brand that has a smaller hole for the column and then bore & broach it to suit a Mini column, though, I don't have a broach and they are eye wateringly expensive, so I'd likely need to make the broach too.
I know I can make (or buy) an adaptor plate but it's just too much of a back yard hack for my liking.
I'll go through the Moto-lita list and that from Locarra and see if I can find something I can work from.