Check this out. Found one of these at work and it does a great job at keeping the water at a steady rate.
SaltWater Aquarium Chiller
They are aquarium chillers built to keep large water tanks at a specific temperature to simulate an ocean environment. I figure if someone hooked one of these bad boys up to a small tank and then ran another loop for their water cooling rig, it shoud work great!
Let me know what you think.