Give as much information as you can, regarding quoting the law, be careful how you explain it, you'll never meet an "official" who is prepared to be told how to do their job, especially if they've been rumbled for doing it wrong.
So explain your toys should be covered by your ukara, a defence recognised under the violent crime reduction act, & that you've imported rifs previously with no problems.
Maybe try to ascertain exactly why they've been held, & if so where the fault lies, because if they dig their heels in, better to be able to prove the seller or the carrier is at fault, in order to pursue a refund or replacement.
& whatever happens, remain polite & respectful, don't raise your voice or swear, even in a lighthearted context, these days there are so many triggers that can be invoked if you enable them.