On a construction project where we have a considerable amount of rebar to bend in a common pattern we would find an expendable slab or flat piece of dry ground, calculate out a segment bend and use a dedicated rebar bender to put a few degrees of bend every few inches, don't use an electrical conduit bender because rebar is a lot stiffer than conduit.

We would draw out the arc we want and do a segment bend, a set number of degrees every so many inches. When we get close we would check it against the arc we drew and add or remove bend as needed. This works for less than perhaps a dozen pieces.

More than that and I would haul the rebar to a welding shop that has a roller bender. A roller bender is, in essence, a set of three rollers that you feed steel into to form a smooth bend. Most commercial welding and steel fabrication shops will have one. Half-inch, #4, rebar isn't really big by construction standards and rolling a consistent bend into it is pretty quick and easy. They might charge you a few dollars a stick. Transportation might be you biggest issue.

I have bent just one or two pieces in a one-off job by stuffing one end into the ground up against a slab or something solid, grabbing the other end, and forcing it into roughly the right shape by leaning into it. If it works your set. The problem is that your bends are unlikely to be consistent. Partly this is just the way of such log-cabin approximations but it also has a lot to do with the rebar. Rebar is usually minimally processed scrap metal and is very inconsistent. One part of a stick can be pretty hard and another, just a few inches away, very soft. Trying to bend the piece in one forced move usually means the soft spots bend and the hard spots stay straight.

Lacking an appropriate bender we have used a sledge hammer pounding the bar suspended between two pieces of heavy steel, the bumper of a heavy truck, or driving the truck onto the bar spanning a concrete curb. Anything to get a few degrees of bend. And then repeating this every few inches according to your segment bend calculations.