I did it solo on Damnation as have others fwiw, you can search topics here , steam or reddit (googlable) for tips e.g. this FS forum post.
There are usually clumps of 4-5 (someone reported 6 in 1 spot once), and a few more a bit further down, you have to gather them all up; 4 or 5 would be insanely easy to do.