Hello Tim,
I doubt that BAS or Aldridge sell seal kits, but the usual suppliers of After Market Parts do. However, the correct, original section seal for the B pillar of a 2+2 is not supplied by any, is my experience, but another section that does the job if it were soft enough, is.
Following are the seal sections used in a 2+2. Don't be concerned that its labeled for a Series 3; they are the same for your car. The seal in the RH column labeled BD28434 is the correct section for the B pillar, but its the seal section in the LH column labeled BD20500 that's supplied by the usual suppliers.
The following pictures show the BD20500 section that's supplied as a B pillar seal. The seal in the pictures is made from two densities of rubber. The area circled in Red in the picture immediately below is quite hard, with the remainder quite soft. If you're supplied such a seal and install it "as is", you will end up with a door slammer for sure.
I've seen examples of this seal with the area shown between the Red lines in the next picture, cut out completely, so as to have the door close without applying unreasonable force. When you have to purchase a seal that's supposed to be fit for purpose and then have to mutilate it, its tantamount to buying a dog and then having to bark for it.
Therefore, I would check with whomever you purchase the seals from as to how the B pillar seal in particular is constructed. The seal in the above pictures was from SNG Barratt. I reported the matter to them, but I'm not sure if they have rectified it or not. This seal from XK Unlimited, now Moss, is made totally out of soft rubber and works.
Regards,
Bill