If you are traveling through civilian ports then you are not allowed to import or export anything that is against the laws of the nations you are traveling through.
If you send your cue through the US mail through the military postal system then you can send your ivory cues as that is technically still within the US Borders. However technically you would not be allowed to take your cue off base in a foreign country where the import of ivory goods is not legal.
I say follow the don't ask don't tell policy.