When I created some new listings a few days ago, I used the 'advanced listing tool' as opposed to the quick one (which is the default for non stores I think) and in the postage section, I think there was the option to exclude locations you don't want to post to, that applied just to that listing.

I was just trying to have a look, but am stuck in another login page loop. I think it's under the postage, something like "create exclusion list" or something that effect......between postage and package type.