I've been looking at the possibility of adding Jaguar Brembo rear brakes to an X-type. During my investigation I came across Tesla Brembo electric parking brakes. Turns out they have the same bolt pattern spacing as the STR rear Brembo cable driven calipers. The STR and some XKRs use 12mm wide solid rotors.
The Tesla calipers are for 20mm wide vented rotors. (Same as the XKR Silverstone rear rotors.) If the offset is correct, one could migrate to 20mm wide rotors.

The Tesla and Brembo Silverstone rear calipers I have fit nicely on the back of an STR hub carrier!
The Tesla parking calipers are going down to $115 a pair. (Could be these are recall era calipers at this price, but they are readily available and 1/2 the price of the STR Brembos.