I think there are 107 RHD MK1's in the UK of which 28 were clubsports. Not sure about the no of MK2's though there significantly more MK2's than either MK1 or RS.
About 240 mk2 GT3s were sold by porsche in the UK, then 120 RS and 108 Mk1s. Then there are all the unofficial imports for all 3 plus lhd cars, probably well over 500 in total.
Andy Duncan is the PCGB GT3 register secretary, he will have the numbers you can contact him via the PCGB website. Alternatively calling Polar Express may be along shortly to help out..........
Never understood Titanic. Been trying to join for ages, every single link on the website leads to an error. Is there some kind of secret link to actually get any info from there?