Based on the case from https://www.thingiverse.com/colsandurz, I adapted only the lid which nearly fit the original HackRFOne case to snap into the original lid. So no need to print the whole case; just print this lid, add the TCXO clock daughter board, and snap on this new lid.

Fits "pretty good", but not as stable as the original lid. If you're careful you can even take the original label off the lid and adhere it on top.