DUMB QUESTION: How do Alpha Legion warbands deal with their geneseed?

So I dont really know how geneseed works in general but as far as I know i think the Alpha Legion geneseed (unless heavily mutated from the Warp) is still relatively "pure"?

I was wondering how do AL warbands manage their geneseed stocks? Can they make more themselves with skilled medics or does it have to be stolen from somewhere else for them to make more space marines?