I'm not sure if this is a valid option with your setup, but would it not be more handy to keep the country name as the actual country name in your country column and then do your reporting based on a country grouping where you mark those countries as "rest of..."?
That would keep your data more correct, allow your maps to work and still keep all your figures grouped.
Also it would mean that if business picks up big time in just one of the countries, it can come out of the group and be reported on on it's own.
I think given what you want to achieve, I'd be tempted to make a merged shape file up, and use the polygon mark type.
What administration level do you need? If level 1, Tableau Mapping has access to Natural Earth Admin 1 data set (free of copyright and restrictions) in Tableau ready format. All you would need to do is group up the countries listed above. If just the outlines, i.e. Admin 0, then that's a lot easier.
Natural Earth Admin Level One, with the countries filtered as above.
I have the same problem. In my case, I need to represent TRIFECTA which consists of multiple countries showing profit over the last 6 months. I also have to represent CN-HK which comes to China and Hongkong. I have to represent both of them. Please help.