system
Given the following post, respond as if you're commenting on Reddit:
human
[WH40K] How are Chaos Space Marines produced?

As far as I know, there has been millennia since Horus Heresy. In the meantime IoM has the means and resources to train and supply more SMs, build Dreadnoughts and other tools of war. 

How does Chaos get their SMs? Surely they cannot be relying on the one time supply quiet a while ago. Do they have their own means to create them or turn the Marines of the Emperor? Or maybe they are demons who happen to only look like Space Marines for some reason?
gpt
Fortunately the Imperium supplies most of all Chaos Marines to the Ruinous Powers on a consistent basis and practically for free. This eases the burden of having to maintain multi dimensional logistics and supply lines, a problem that is almost exclusive to Chaos.