tk2d loads @1x and @2x sprites from Assets/Resources/tk2d
By parsing the content in there (by loading as assets), you'll be able to figure out what each asset points to (1x asset, 2x asset, etc).
To create a build without any 1x data, all you'll need to do is the above, identify all bits of data to get rid of, move the assets OUT of the resources folder. You can then build, and once you're done building move those assets back. You should be able to script the entire thing.