Hosted here: http://migrants.python.coffee/
The data used is provided by un and can be found here and here
Creating topojson files.
get the shx file from here https://github.com/nvkelso/natural-earth-vector
ogr2ogr -f "GeoJSON" spam.json file_name.shp -select "iso_a2,name"
topojson -o topo.json spam.json --id-property iso_a3
Then you can use http://www.mapshaper.org/ to shrink the file