I finished mine some weeks ago!
Passport
No. I have to do it legitimately.
Although, I was playing a Daily Game with someone from the Marshall Islands, and he switched flags during the game. I asked if he would switch back because I was worried it would only count the flag when the game ends.

Oh, well done! Do you have any advice?
PS - I see you have 33 Book Openings, too.
I also did it legit and only playing daily. It took me months to find the last few! Ultimately I used the API to list players from the missing countries and try challenging them.
Has anyone filled in every flag?