I am playing the game on the hardest difficulty and see no possible way to get this achivement. I get 2 eliese and 1 roaul and to no achivement. I have also gotten 3 eliese and still no achivement. Is it only counting the 10 knights in which case I can only get 30 at best and still 15 short. I can find at most 1500 gold.
Scout around the whole map. You’ll find more treasure chests - enough to call sufficient knights.
There’s an easily missed one at the start of the side road to the enemy castle. To the left of the upper town.
The unmounted knights count alongside mounted, so that should be the only types you’re buying.
Last option on the list.