I get raw stock suitable for this project , every time I tear down a chimney and fireplace. It's available for free in Victoria.
There's a much more suitable recycled material available for making tines. Planer blades can only be sharpend so many times before they reach a point where they don't fit the machine . It's different for each type . Some of the big commercial units used here on the west coast, have a blade large
enough to build a froe. Smaller models are perfect for making a broad fork. They are made of really tough metal that is pre-drilled. This would give the option of attaching them to a hardwood block with a handle similar to what you would have on a mattock. A workable broadfork for the millions of people who don't have metalworking tools or skills .