You might want to try the DNR website sometimes if you can't find a private range the DNR has public areas you can find, they do this in IA and im pretty sure South Dakota does the same thing.

Also if you don't find anything right around Sioux Falls look in SW Minnesota or NW Iowa or NE Nebraska. You would be close enought to visit any of them with little fuel spent. if you have a SBR or a supressor stay out of IA with it.

Best of luck, Sioux Falls is a nice place.