You can buy them from a concrete supplier. My husband made a bunch of his.
He took pvc pipe and cut it, like he said you need to be sure how deep the concrete is or it could push the rebar above the concrete. Then he put 2 pieces of wire in the pipe and poured concrete in it and let it set up, so pretty cheap little ones.
I asked my husband and he said in our motorhome garage its fiberglass
fibers in the concrete and no rebar, been over a year and a horrible winter, no cracks yet.