Lost Berserkers since 2014 are reachable also during Hero of Rathleton Quest. You can find a few of them in three different areas:
1) area before Deep Terror boss cave:

2) area before Glooth Horror boss:

3) area before Raging Fires' room:

Unfortunately, this area also requires quite a bit of questing. As many as 500 votes and the rank of Rathleton Squire are required.