Martins especially have fairly consistant prices throughout the US.
Guitars from dealers that you can repair and resell are occasionally available but usually are marked up so that they are selling for what they would fixed, minus the <wholesale > cost of the repairs....i.e. the store is taking the profit and not actually investing in the repair.
Far better is Ebay, though you need to know what you are doing and how much to pay in order to make it worthwhile. Those I know who buy from Ebay to resell usually confine themselves to models such as D size guitars from the 50's and 60's with problems which can be rectified without obvious signs of the repair. Bridge replacements, neck resets, refrets etc. can be done without impacting negatively on the price of the guitar.
Poorly refinished items, bad cracks or breaks as well as anything unoriginal (except perhaps tuners) is usually avoided.
Often stuff sells for a shockingly high price on ebay too, especially if it's busted. We have a running joke that if you want to sell a guitar on ebay you'll get more money for it if you break it first.........(of course we'd never do that....)
Anyway, depending upon your skills and the value of these things across the pond, it might be worth your while. Shipping and import duties on your end are a factor too.
If Martins are you main interest, I'd check out the UMGF forum (Unofficial Martin Guitar Forum) they have a Buy and Sell listing which might help get you started.
http://theunofficialmartinguitarforum.yuku.com/