BWprice100, I have to disagree with your comment about threading dies as that has not been my experince, but perhaps it is different in the UK.
I'll second everything Rich said and add that I think that considering your particular needs and time frame, that it would be a mistake to attempt a retrofit.
As a person who has started, built up and sold several businesses, and owned a small specialty machine shop, I can tell you what I would do in your sitaution. I woud consider these two options:
1) purchase a wokring used CNC lathe from a shop, dealer or hobbiest that can demonstrate thread cutting of YOUR threads on YOUR material. If they won't do that, then assume that they can't.
2) lease a new CNC machine. Tax incentives and depreciation on new equipment (at least this used to be the case here in the US) is far greater on new equipment than used, so the governement helps you buy the thing. Make the lease payments out of the profits the machine generates and save your cash.
Enjoyable conversation . . good luck with your project!