Augustus,
Lots of people have made them, but I bought mine with the tractor. They work pretty well, but one problem with them is that it is hard to see the tips through the bucket, so you have to stand up to see what you are doing.
Once you get under what you want though, they seem to work pretty well.
Another thing. The ones I got do not slip over the toothbar, so I have to take the toothbar off when I want to use them. That is not a major issue though, as the toothbar comes off in about a minute once the wrenches are in hand.
Hope this helps. There have been some threads in the past with pictures of clamp on pallet forks. A search might turn them up. I remember one by Harv that had some good pictures of the same kind of forks as I have...