If I am picturing this corretly, I think there is nothing on the market because it dont sound like a good way to mount an implement but it does sound like a good way to tear things up. All the weight of the 3PH on a little reciever tube mounted in the middle of the bucket??
Basically, if I understand correctly, you want a 3-point hitch hookup, mounted on a "frame" of some sort, with a 2" square stub that you could insert into a reciever tube mounted on the fel bucket right??
What exactally are you trying to do??