If you explain why the source isn’t trustable, that’ll work for some people. But the people who wanna shout “but china bad” at the mear mention of it will just ignore that. So, ultimately - and unfortunate as it may be - this is one of the things that a hard stance must be taken on, and will likely be disrupting to your community. I.E. you’re gonna have to remove any and all posts with these sources, and possibly ban users who repeatedly try to use these sources.
You should probably find some active users to appoint as moderators, to reduce your workload.