Get the Superior National Forest map. It will list both campgrounds and backcountry sites. Spend a little time looking it over and you’ll find lots of options.
I’ve camped at most of the sites inland from the Sawtooth a few miles. Including a couple that require a short hike or paddle to get to. Baker, Dumbell, Whitefish, Wilson, Sawbill, etc.
Only note on free sites is they are first come first serve. From when I started finding this area in the early 2000’s it’s much harder to find an open spot now.