Hi Snoopy. I'm with 2 clubs, the JEC who have a great monthly magazine and superb information back up but they cater for all models. Saying that they have well over a thousand XJS owners.
2nd club is one that I have just joined which is a brand new club exclusively for XJS owners, its called XJS club Midlands. It started off in the Midlands area but is rapidly expanding (members in Australia and Tasmania) so I think maybe a future name change might be appropriate. There is a one off payment of £10 and some very knowledgeable members in it. If you go down to the XJS section on this forum, look for a member called mickblain and PM him, he will give you more details, unless he has already pick you up on here I'm sure mick will contact you. Remember this club is just for XJS motors.
Dave