You could buy it from somewhere like extra efi mate, that will come with a brand new loom taht you make fit.
The other option is to fit a ford efi wiring loom from a fiesta rs turbo or 2i and fit a ofam ecu from boostmonkeys which is what I'm doing.
The first option will be better as you get a brand new loom to start with but the second option is a better made ecu as its in oem quality enclosure.
I went with ofam as I already had ofab management fitted.
Rob at boost monkeys is working on an ecu that will replace the mfi system on rs turbos using the existing loom with a few alterations, mibbie worth waiting for that if you can?
Have a look on his site for more info, try emailing him too. He's very helpful