Here's a great map showing all POSSIBLE locations. Sometimes there will be none active. Sometimes there will be more than one of each.
Also here's a great post to keep looking at because people are posting the active social events. Just look at the latest posts.
https://acinitiates.com/forum/discussion/4641/page/1All credit to the original websites.
Edit: Thanks to "A Gamer X360" for his comment that provides a info on the "Cannot connect to uPlay error" and additional info about finding the events yourself. I haven't tested this out myself because I haven't received the error but should help some people.
Single Player "Unable to Connect to Uplay" Workaround