Try calling Deems Equipment in Marshall MO.  They are a JD dealer and seem to have quite a few of those in the area, usually ahve a traded 12r on the lot.    We had one with the hinge in the middle, could drive right down the top of a terrace and put 6 rows on each side.  Sometimes there are issues with the planter raising and lowering evenly, looks like a bat flying when going up and down but if that doesn't bother you they will work great.

I believe Deems bought the jigs from the place in IA and started making these bars, not sure though.