There are alot of wrecks along the west shore of lake Michigan. What is your experience level? How deep of water are you comfortable in? A good starting point in Milwaukee would be the Pirates Cove run by a fellow named Jerry Guyer. He runs a boat called the Lender which is slow, but comfortable. He goes to The Prinz Wilhelm ( the Willy), the Car Ferry Milwaukee, and the 906 Dredge on a regular basis. Divers Delight Charters out of West Bend goes to about everything from the Wisconsin off Racine to the Hetty Taylor off Sheboygan. Fast boat, no frills but good people.
I would suggest that you look into the club scene. A great way to network. You might find your way onto private boats this way. That would give you a bit more flexibility. You can meet club members at functions and decide who you want to dive with that way. I am a member of the urge to Submerge club out of West Bend. I found them doing an internet search for dive clubs. Give it a shot. Might be worth your while.
Jim