I don't know what their hours are, of if they're even open this time of year, but there's a dominating fireworks shop in Bad River, WI.

A neighbor of ours sometimes goes to Victory Fireworks in Danbury, WI.  He has brought back some pretty entertaining stuff from there.

If you're looking for safe fireworks (that don't go up), they can be found around most of Minnesota a few weeks before July.
If you're looking something bigger, I'd also suggest Victory Fireworks (rumor has it the bigger stuff can be found in the central Wisconsin stores that aren't near the border).
As long as you are are using commercial fireworks and your common sense, you will be perfectly safe. Many firework accidents are the results of stupidity with commercial or homemade fireworks (ie: don't mix your own and then hold it in your hand).

I know people who set up a stand in the Miller Hill Mall during the 4th of July and will send this link to them and they (I'm sure) will contact you.