The tubular heaters for Lyman pots came from a company called Tempco. My spare Lyman element is marked "THE04963, 800 W (Watt) 120V, A 09 14. That big honkin' pot of yours would need a much longer heater. I've heard Tempco is spendy, but I have never dealt with them myself. They would probably only offer heaters is straight lengths that you would need to bend with a tubing bender, but this may be doable.
Waage may be an option too, they do make pots that size but I don't know if they'd be willing to try to help out someone with a competitors pot. I believe that Buffalo Arms used to sell Magma pots, they may have some ideas as well.
A web search for "tubular heating elements suppliers" turned up many, many hits as well. These elements are very similar to the heating elements in electric ovens, but you'd need to be certain to get one that is 120V and not 240V of course.