I'm trying to figure this out for some friends that have Macs in Greenland and Papua New Guinea. Selecting Denmark does not work for Greenland and there is no store in Papua New Guinea at all.
Didn't realise the mac app store was country specific, learn something new every day (yesterday's lesson was not to use a shower with no numbers on the temperature dial)
Set up a VPN for them to access whichever countries they want to access it at. They would also likely need a credit card from that respective country as well.