Hi,
I find it a little strange that the Tinkerfolly gnomes sell Ballista, Catapults, Ballista ammunition but not Catapult ammunition. It means you can buy a catapult, but you need to wait for the random artillery merchant if you want to be able to use it, unlike the Ballista. Would it be possible to add ammunition to their stock? Maybe only the weakest kind, and you can get the better kind from the artillery merchant.
Done.