SCCA specs the XJ6 calipers and vented rotors on all the Tr3-Tr6 models. Part numbers listed in the PCS (rule book) are
Disc: C32764
Right side C: 60-12797
Left side C: 60-12796
The SCCA cars are running aftermarket hubs and I believe they are requied in order to get them to work (or stock Jag hubs). Not 100% sure on that though. They are more effective than the stock Triumph peices for sure, but parts are expensive, and for competition use the seals are melting (talking road racing here), for street use or autocrossing they would be fine.
I've heard of people spacing to the stock 16P calipers in order to fit vented disks. From what I read they were common fitment on Fords in Europe with vented disks, and all was used was a spacer.
That should get you on the right track. Hoepfully someone who has done this on here chimes in.