I can still see Wales in the latest download (if you are talking about garmin.openstreetmap.nl).
Try clearing your map browsers cache (ctrl G twice in Mapsource or Basecamp) if it is the pc version. If it is on your device, make sure you have removed older versions first.
Wales is not a separate country, it is part of the UK map, please zoom in to Wales and it will show up on the map.
If that still does not work for you try another map provider: https://extract.bbbike.org/?format=garmin-osm.zip