In reply to walts4:
At the risk of stating the obvious, Cotswold's Exeter branch isn't too far out of your way, and doesn't involve driving into the city centre.
Cotswold Truro is another option, although that is right in the middle of the city.
You might struggle to get the definitive Pembroke guidebooks in either.
Edge of the World in Penzance is a good option - phone them on 01736 365607