Are you looking for amphipods or copepods? I've got a million amphipods. I was trying to increase my copepod population and bought some online. I dont know how well that turned out as the ones I recieved were so small I could barely see them in their little container I doubt I would be able to see them in the tank/refugium. There are some good size copepods in my little puffer tank that I am going to try to siphon out for my main tank, but I doubt I could get more than 20 or so. Anyway, I dont know how much help my post was. One question I have though is this; could an exploding population of amphipods have a detrimental effect on the existing copepod population?