If you are a software developer, you can download the entire Club Log exceptions and prefix lookup data. This is encouraged as one of the driving reasons for Club Log's existence is to increasing logging accuracy, You are very welcome to use Club Log to take the chore out of this problem.
This is the recommended method for getting the DXCC of DX Cluster or Skimmer spots.
The address is: https://cdn.clublog.org/cty.php?api=APIKEY (updated daily).
The file format is XML. You can download the XSD schema here. The file is supplied in a GZIP archive, but if you need ZIP you can add zip=1 to the URL:
When you download this file, you need to supply your API key. This can be obtained by emailing the helpdesk and providing further details of your proposed use.
The Club Log XML file is free but it would be appreciated if you could help promote Club Log if you incorporate this data into your logging program.