Getting close to the end! Luxembourg, the Ukraine, Vietnam, Laos, Nepal, Ghana, and Uruguay are probably the easiest ones to strike off as all should be findable in any 50c or less world coin bin.
For most of the others, a good challenge would be getting a circulated coin - while it may be tempting to buy a NCLT (this includes BU circulation coinages that are primarily made for sale to collectors in the West) to fill in a spot, I found it very exciting when I was able to come across circulated examples for tougher countries - my Sudan piece, for example, was from the 1970s but only G/VG.