Do a makeshift lathe trick wind the bolt all the way into it, then put the bolt into a drill and press the trigger. Then while the starnut is spinning really quickly you rub the file on the flanges of the starnut, it wares it down to 7/8.
Have you tried Scooter Garage- I think they are in SD.
Aces n Eights have them
http://www.acesneightsscooters.com/ICS-Starnut-ICS-STRNT.htm
Even though it states ICS, just go in to the menu and select 7/8" when ordering.