I press Ctrl + A to select all the marks on the map (or Area select them) and then right-click a mark and select “View Data”.
Now I have every zip code within a region along with the associated Latitude and Longitude. Now, simply press Ctrl + A to select all rows, then Copy, then close the dialog box, then Ctrl + V to paste back into Tableau as a new data source!
http://vizpainter.com/poor-mans-custom-geocoding-in-tableau-part-2/