Flip Over Shanty Sled Repair
Not sure if they still do it and if they do,just how expensive.
But the seamstress/tailer/clothing repair shop in Waukesha that I regularly use probably would be capable. They've got big power sewing machines for the thick canvas... I'm certain that the leather shop/cobbler I use in Waukesha could also handle it.
Don't know the names of either but point is that there's probably someone near you in Milwaukee that can handle the job. Maybe look in YP online for 'alterations' or 'sewing'.