I don't see the issue of getting a handful of pre-made or homemade explosives, especially for a state sponsored actor, it's not like you need a large amount. If all else fails, strap a molotov cocktail to the drone for a incendiary device. Hard to control the sale of petrol.
If we're talking about a isolated attack on a single ship, just for "terrorism", then sure, the requirements aren't onerous. But what does that get you? An operation that does nothing in the long run with the possibility of being traced back to you and all the egg-in-face that entails.
If we're talking a strategy involving the use of about a coordinated D-Day against ships in port and planes on deck and in air bases then that's a whole crap ton of explosives. You just need one cell to get tripped up to set off a cascading hunt for the others. Like I said, lots of tripwires focus on explosive detection. Very little, outside of HUMINT, picks up inert stuff.
Now, truckloads of swarm UAVs to 0-day say platforms and bases in Japan, depriving them of sensors and airframes, should they decide to get involved in AR? That's something worthy the direction UAV use is heading.