I welded it up from scrap I had in the shop (bed frame angle iron, black pipe, square tubing, shovel handle). Lots of different scrap will work. Make sure to make your forks wide enough so you can get around a 4 inch stringer.
In the beginning, if your pallet boards are too close together to fit the breaker, go ahead and knock the first one out with a hammer from behind.
Bed frames and old yard tools are great raw materials. Cruise Freecycle.