if you have any marine algae you will get them living in that. Refugiums with Caulerpa and other common macro algae make ideal homes for them. You also get them living among rock but mostly in plants.
I had a 4ft tank that was half Caulerpa and every week I would remove a 5 litre bucket of the stuff. When I lifted the Caulerpa out of the tank and bucket, numerous copepods would drop out of the plant. the fish loved them