I am not sure where you are in MI, but I bought mine from Michigan Spray Foam.
There is one listed on Ebay, search for side arm exchanger, or plate heat exchanger. I have the side arm type. It was explained to me why the one I have would work better than others I would find, but it has been a couple years and the details are fuzzy. I think it had to do with the way the tubing was routed inside, coiled instead of straight through.... Sorry that is not much help.
I purchased both of my water to air exchangers from freeheat4u on ebay, he was very knowledgeable, and willing to help and carries all types of heat exchangers.