It's a good idea but I've been scratching my head on how best to do it in a way that would make it easy to use without being onerous to implement.
A thread per region doesn't really give sufficient granularity of location but extending this to (say) county level would be too much work for too little gain.
The subject is generic and doesn't need a tie to Mk2/3/4 so I was thinking of a new dedicated section in the non-technical area which could be entitled "Vendor Recommendations". I choose the word "Vendor" because there is no reason why establishments other than garages shouldn't be included (paint shops and wheel alignment specialists are a couple of examples that come to mind).
Placing all recommendations as individual threads in a single topic area makes the implementation easy, but members still need to be able to filter for those relevant to their location (assumed to be at county level for now). This can be easiest achieved by forcing the inclusion of location in the thread title and perhaps making each thread subject to moderator approval before publication to ensure this is done correctly.
With this in place, a member will only need to search the topic for all instances of location x in the title and they will find all recommendations for their chosen area.