We recently had a requirement to execute a plugin when a CampaignActivity is distributed using “Distribute Campaign Activity” button.
As it turned out, this message was not available.
As it was on premise, we enabled it in an unsupported manner i.e. by updating the sdkmessagefilterbase table in orgname_mscrm database.
SQL Query Used :-
sdkmessageid=(select sdkmessageid from sdkmessagebase where name=‘DistributeCampaignActivity’)
Hope this helps.