How do I find a flight from Milwaukee or Chicago to Laughlin, AZ?

I have not been able to find one.

You don't . You fly into Las Vegas -LAS -rent a car and drive it .It's kind of a neat drive actually .The best part is when you make the right onto US 95 from US 93 and you're looking 50+ miles down this little ribbon of 2 laner
If you don't believe me go to http://www.airnav.com/airports and enter KIFP in the box that asks for airport
Open that up and click on Book A Flight

Actually, I've always flown into Bullhead City, AZ airport, which is just across the river from Laughlin. We have direct flights from Des Moines to there and I simply hopped a bus from the Bullhead City airport to Laughlin.

Riverside Resort is who I have previously booked with. Report It

I think that she was looking for regularly scheduled flights . I'm sure that if you promise to donate early and often to the casinos welfare fund that they would arrange to fly you on corporate aircraft from just about anywhere Report It

did you try southwest airlines?

I believe that Laughlin may not have an airport and if they do it will be small and many of the commercial airlines don't fly there. First, try the smaller, discount airlines: Southwest, Airtran, America West, Skybus, Frontier, Jetblue, etc.
You may have to fly into LA Vegas and drive to Laughlin which I believe is only about 2 hrs.

GOOD LUCK AND HAVE FUN