I looked for quite a while before I finally decided to fabricate one myself. I used a 30” section of 4”x4”x3/8” square tubing and I cut out two 6”x6” steel plates. I punched (4) 5/8” dia. holes on a 4.5” on center bolt pattern with a mag drill. The pictures are from before I replaced all the bolts, the wheel studs were a temporary measure to get it all hooked up and out of the middle of my driveway!
I made the articulating crane in the picture too for the heavy pieces at the end of the day that won't go through the chipper!