Simon's original content - fun read - but takes time to understand.
Excellent portal dedicated to Wardley Mapping operated by equally excellent Ben Mosior.
This is the community hubs that contains a lot of community content.
Simon is currently migrating multiple Slack communities to one Discord server. This is not yet public, but you can ask Simon for the invite. The community is centered there.
5:51 Youtube video explaining the concept, with 1.6M views, excellent quality.