$ ./geoclue-mlsdb-tool_mcc310316 -c Spain MLS-full-cell-export-2021-01-17T000000.csv
Reading data from file and caching cell locations which are within the bounding boxes...
Progress: 11440000 lines read, 2371172 cell locations inserted
Finished reading data: 11447488 lines read, 2371172 cell locations inserted
Writing data (596603 entries) to mlsdb.data file: ./1/mlsdb.data
Writing data (569987 entries) to mlsdb.data file: ./2/mlsdb.data
Writing data (497477 entries) to mlsdb.data file: ./3/mlsdb.data
Writing data (358144 entries) to mlsdb.data file: ./4/mlsdb.data
Writing data (155940 entries) to mlsdb.data file: ./5/mlsdb.data
Writing data (67372 entries) to mlsdb.data file: ./6/mlsdb.data
Writing data (43605 entries) to mlsdb.data file: ./7/mlsdb.data
Writing data (38372 entries) to mlsdb.data file: ./8/mlsdb.data
Writing data (43672 entries) to mlsdb.data file: ./9/mlsdb.data
Done!
According to https://en.wikipedia.org/wiki/Mobile_country_code US MCCs are 310-316 (excluding Guam and V.I.).
US cell data as of 2021-01-17: https://gofile.io/d/lkmFp4
PS You might need to devel-su chown root.root -R /usr/share/geoclue-provider-mlsdb/
afterwards.