I've been contemplating building one, but so far the local "stick mart" has supplied everything I need.  I have two boys and they love whittling the bark off of a walking stick.  Invariably, they'll give me one for the fire until they get one perfected for walking. 

But now you've got me hankering to weld one up again.  ***sigh***  The work of a tinker-er is never finished.......  😉

Like other posters, we use what's free & found, usually a sturdy (but damp) stick.  However, my MIL recently gifted us with a BBQ fork that's frighteningly large (can't imagine using it in the house or with individually-sized cuts of meat), so we use that in our home outdoor fire pit.  She found it at a discount store (Ross, Stein Mart, Marshalls), it's made by Bodum and is pretty sturdy.