Hello there!
I live in the Milwaukee area, and buy all my fish at Pets 'n Things in Cudahy. It's a small store with very knowledgable staff. Their assortment isn't that big, but they will order for you. If the fish they get for you don't look good, they won't make you take them.
A very nice looking store is on Hwy 100, can't quite remember the name, but it's huge. Let me know if you need me to find out the name. They have a lot of saltwater fish, as well as a tank with some huge fish to show people how big they get. Very impressive. Don't know much about their staff, just went in to browse and look for Puffer fish.