Trouble is the post office now intercept radium instruments and stop them being forwarded on. Buyer or sender has to collect from the depot which they have been stopped at which can be a hundred or so miles away. Post office now have detectors to combat radio active items being sent through the post, radio active aircraft instruments are also on their prohibitive list. Sorry to be the bearer of bad news ! This can also effect Ebay sales unfortunately.

Seek specialist advice where necessary. Some emitters are hardly detectable (notably alfa only) if properly packaged. Depends on what you ship where and how it is packed. Others can be a pain. There was a case recently where a containerized aircraft from the US into the Netherlands was seized because of radioactive instruments, quarantined and the instruments destroyed by a specialist company at the owner’s expense.