How does one access Kosovo in the natural earth ne_10m_admin_subunits shapefile? It seems to lack the "XK" code needed to access it.
From an inspection of the file it appears that Natural Earth doesn't assign an ISO code for Kosovo (-99 is used). You could find it using any of the following key/value pairs
adm0_a3_us KOS sov_a3 KOS adm0_a3 KOS gu_a3 KOS
I suspect it is related to the note
Self admin.; Claimed by Serbia and the there is further discussion at http://www.naturalearthdata.com/downloads/10m-cultural-vectors/10m-admin-0-details/