Nearest I get to an "owners club" is here...
http://www.bmwland.co.uk/talker/
However I'm also involved with one or two local motor clubs due to my rallying interests. Now I guess a typical local Motor Club has 100-150 members and is affiliated to the RAC MSA (the Governing body for motorsport in the UK) so they can run events - rallies or whatever.
More to ther point, if my experiences are anything to go by, they almost universally produce a monthly paper newsletter, for which some poor soul is permanently
pleading and begging for copy! Given that you can take support within such organisations virtually as a "given" I would go as far as to say that you'd probably have no trouble whatsoever getting a page a month FOC in the average motor club newsletter in which to propogate the message.
If you were to knock some of the resources you already have into easily digestible articles covering the basics I reckon your average motor club editor would lap it up.
I think there are about 500-600 affiliated motor sport clubs in the UK - I can get my hands on a list of secretaries...