Since no one posted a lead on a machine, would you consider using a hemstitching attachment instead? the main issue with them is that you need to make sure the PLATE fits the machine, the unit itself can be used on just about any low shank machine.
It would be a much lower cost alternative than to buy a machine specific to hemstitching, I would expect there are industrial machines that only do hemstitching, but I'd expect them to be on the expensive side.