Dwarf Cannon engineer does not restock Cannon ammo mould

Asking to buy cannon parts from the Cannon engineer near the dwarven mine opens up his shop, which sells cannon parts, the instruction manual, and the ammo mould. Wiki says he stocks 7 ammo moulds (https://classic.runescape.wiki/w/Cannon_ammo_mould).

His shop had 0 moulds in stock for at least a 20 minute time frame - I didn't buy any moulds and nobody else was nearby to buy them either. Looks like they aren't automatically restocking.