I've done one of these twice since 1.19, both times at Emerald Moss. Apparently they pop at the lvl 10 camps now, and there is a separate cheevo for each. I've no idea on the timing though. But there is an NPC in Grid that talks about an invasion during the recruitment phase, so i suppose there is an npc in each city that does that for the respective lvl 10 camps when it's about to start. There's also an NPC that pops at the camps themselves and tells you the general direction to go to meet up with another NPC to actually join up.