Claimed:
United Socialist States of America: Crezth*
Estados Unidos de Latin America: Shadowbound*
Vietnam: DarthNader*
Union of Islamic States: Amon Savag*
Federal Union of South East Asian States: Masada*
Pacific Union: Banana Lee*
Unclaimed:
Union of Latin Socialist Republics: Warhead
Indian Empire: Gelion
Russia: das
European Union: Fuschia
Japan: Skizzik
Nigeria: andis-1
People's Republic of South Africa: charles_li
Of those, there are a few who haven't been as active lately, and whose countries you could have a good chance of getting. I believe Fuschia, andis-1 and skizzik have been pretty absent lately, and I don't know whether or not das is playing in NESes recently. I don't know about the presence or intentions of Gelion or Warhead.
If Fuschia doesn't return, Milarqi gets EU. Other than that, I suggest Adrogans and Omega124 to make claims to other unlikely-to-return nations.