Playing as any of the Beastmen Lords, I work my way up to unlocking any of the special chaos bestigors, such as khornegors, pestigors, and so on. But I don't understand how to recruit them. They only appear as recruitable from the global recruit tab but the lords don't have any global recruitment slots to recruit globally. I've also tried being garrisoned in a herdstone with the special units unlocked from it's sub building. Am I missing some way to recruit them?