Apparently, there's a dragon-worship Church on North Continent, which considers hunting dragons (or using them as material) a taboo.
Also, because of the climate, there are almost no land dragons there. There are water ones, but that's not convenient for mass hunting. So, they don't really hunt dragons in North for both those reasons.
Freya's country doesn't follow that church, so they actually want dragon goods.
However, South countries know that "Northerners don't want dragon goods" so they don't usually export them.
So they are surprised by Freya's request, and just don't have enough prepared on hand to trade. To the regret of both sides.
Remember that all this stuff needs to be processed and transported, you can't just go hunt and give fresh corpses.
They still make huge profits from trading Northern iron and fur for Southern spices and sugar. Freya mentions, if only 1 of 3 ships survives the journey, it's still profitable.