Pillbugs are extremely hard and rare to catch because once they spawn they can enter and leave levels having them hidden away in buildings. No easy way to find them other than looking everywhere. I got 3 of my 5 from going about the railroad. 2 being on the rails, 1 in lowest level of bandit cave, 1 was found in that house by mod with the golf course downstairs and the last one was in some other house in mod