There are a couple of sites ran by southwest wargames mate, one at the old shire horse centre, one at screasdon fort and fort tregantle too, also MIA near bude and a site in exeter, Im sure newquay aswell.
Having not played for some time I are southwest war games still going? I hope so. Anyway they always had some good stuff going on. Also there is a place in Bristol, Exeter and Newton abbey that you could give a go. I have been to all the above and they are fun.