This will find dependencies from a selected package or definitions folder and export them to Excel:
This will read the Excel file back in, and compare with node names in your Packages folder (may take a while):
Both of these dyns can be run in standalone / sandbox mode.
If there are missing nodes, they should appear in the pink box. You could then go to DynamoPackages website, download previous version that had the dyf you want, and then copy the contents of that dyf into your own custom node.