I’d like to be able to set up this feature! It was discussed here:
Currently, the main unicycle events calendar (as far as I know) is Open Unicycle Calendar | Teamup and it’s reachable via this forum’s icon: 
@makym, the rider who’s in charge of this calendar, also replied in the discussion I’ve linked.
The key points are: he would be okay to have the calendar somewhat migrated on the forum, but certain features need to be kept.
There are events/calendar plugins for the forum software, but they lack some of the wanted features and I don’t have the technical skills to add them.
So, I can’t do much know, but I’ll let you know if something changes and I’m of course open to any idea. 