I don’t believe that there is the ability in Discourse to have aliases in the manner in which email aliases work.
All I can suggest for the moment is if the Example Co-operative, example.coop, had a general contact email address such as contact@example.coop then a Discourse account with the username Example could be created and then you could @Example and this would trigger an email to contact@example.coop.
You could suggest / urge co-ops to setup accounts like this I guess?