I would suggest you can use GSS files but might find this answer posted in another thread which might be easier:
"A couple of things that might help. Tableau today, supports a definition of second level administrative units in the UK, which include Counties, Unitary Authorities and Local Authority Districts (incl. ONS and GSS codes). If that is not what you are looking for (I know not all Counties will map in Tableau if you are expecting something like 380 counties), then I would suggest downloading the shapefile that you are looking for from the Ordnance Survey or other geospatial portal that you prefer because Tableau supports connecting directly to spatial files, including Shapefiles."