The current version of Mkgmap does not provide a very functional address search. This is because of limitations in the understanding of the Garmin map format and your country selection problem is likely to be a result of that. Luckily it seems there has been a major breakthrough regarding the address search in the last few days. I guess I’ll upgrade to the latest Mkgmap for the next release (in about 2-3 weeks). I have good hope that your country selection problem will be solved by then.