Membership is open for all Toyota 4WD manufactured vehicles, up to this point 98% of the folks that have joined are either FJ Cruiser or Land Cruiser owners...
Same situation from a national perspective.
http://tlca.org/membership/info.shtml
You are correct there are other vehicle specific clubs out there but even the Tacoma Territory Off-Road Assoc, rebranded themselves a few years back to be the Toyota Territory Off-Road Assoc...