I use 1/2" .028" wall 4130 seamless steel or stainless steel tubing I buy from several tubing supply houses. Then I bend it with a Swagelok hand bender.
I've bent .058" wall 4130 seamless and .035" stainless steel by myself with that bender. Regular 1/2" .028"/ .035" wall DOM steel tubing would also be fine and a lot easier to bend.
Tom