OK you are looking at copper tubing -like you sweat (solder)together. Soft copper tubing is regularly available in 5/8" Dia. It is soft enough that it is sold in rolls in boxes.
You can easily bend it in your hands but if you want tight radiuses you do need a bender...or even a long spring that just fits over the tube
I have a set of benders made this way and they work pretty well. Get an extension spring so it will have a lot more coils to support the tubing.
Tubing benders are available pretty cheap also. My local Carquest sold one this week that would do 1/4, 3/8, and 1/2 for $7.00. And it was the type with a moving arm which is much better than the one piece units.