I am also a member, retired and living in Thailand, Phayao, but my P6 sty in UK for use when I visit. Some years go when I lived in Bangkok, I saw another P4 n he road, but just a passing car. I met a P6 Thai owner hen looking at his car, parked in Chula Uni. grounds. I believe that there are other classic Rover about the country, but I have never seen any.
Do you have any contact with the Lufthansa Classic Car Club, in Bangkok? They used to have a annual meeting at thee army base in Bangkok, and I went once. Great selection of cars. I have never heard of another meeting, but odd mentions in Classis and Sports car, (Simon Taylor,) suggest that the Classic scene is flourishing in Thailand.
In Thailand, I am sorry to admit that I drive a Toyota Vios. Efficient modern car, that has shown up the poor gear change of my Rover.