[Gandalf Parker]

Gems come from magic sites, and slaves from magic sites are treated the same.
Since blood hunting is a commander action, it goes into the commanders ownership.
I guess you could create a magic site that allows gem collecting by assigning a commander to enter the site.

The comparison with gems came up later. The initial image I had was the problem of having blood commanders in a province that didnt have blood slaves for personal use. Collection was all or nothing. Keeping just some on the commanders was quite abit of micromanagement.

I hadnt actually considered the other option. Generally I just do blood collecting at labs.