I would suggest someone has not been greasing the 12 U joints. The damage shown is what happens when one end of the U joint doesn't exist anymore.
The part you want is described as a flange. The NSN is 2520-00-678-3109 with a US army part number of 7370695.
They will be out at the wrecking yard....they are parted off 30 M151A2s I bought for $110 each and stripped down to the body shells. I actually got word of the success of my purchase of these while I was on my first honeymoon back in 1987. That marriage turned out to be my shortest.
Unfortunately, I do not know when I will be out that way again as winter has begun to set in around these parts. If you are still looking come spring I can help you out. However, with those part numbers, you shoudl be able to find them on ebay or from one of the military surplus dealers in the US.
http://www.ebay.com/itm/2-M151-M151A...p2047675.l2557
You will also find that when you take the hub apart, you are going to need to repack and likely replace the wheel bearings. The M151A2s are notorious for bearings.....they are either dry or they are working loose.