Is there a juicy discussion board like HN that discusses management?

You don't say what kind of management, but if its general people/organisation management then https://workplace.stackexchange.com/questions/tagged/managem... might be useful. Not sure it qualifies as "juicy" though...

If someone wants to create this I would super gladly join.

Specially if it has a section like Ask HN.

I really love Ask HN as it gives me a peak into real life questions or struggles. It makes this corner of the internet very human.

How about HN? We discuss management fairly often.

Glassdoor?