I'm new to 40K and reading up on heaps of background and lore.
Currently going through the Horus Heresy and its consequences, and some questions popped up.

Since most Space Marine legions that fell the Chaos lost their homeworld and were subsequently driven into the Eye of Terror, where do they find new recruits?
From what I've read they scavenge equipment and power armour from each other and from fallen loyalists, but where do they find new troops that live up to the high Space Marine standards? And do they even have the right equipment and medication to go through the entire process?