You can’t get hold off them due to their rareness. You can’t construct them without the huge magic core acquired from monsters like dragons and upwards.
It was also the reason why I was forced to sell the magic cores, I obtained after defeating two dragons, to the kingdom two years ago.
“We will leave the further investigation to the kingdom.” (Burkhart)
“I guess it is not good if we don’t go and see the state of the underground ruin as well.” (Wendelin)
“Those golems and such, they won’t be restarted, right?” (Ina)
“Who knows?” (Burkhart)