Carbon Arc and their parts are available on the web, and for sale on eBay! Just Ordered four of these rods. They are 12 inches long, half inch in diameter. I am very curious to see how much continuous arc can be had with these. If one can get 24 hours - that's two hydroponic days. Cost - six dollars a day. The price drops quite a bit if you buy in bulk - just $3.62 apiece if you buy 100 or more. Depending on just how long a pair lasts will determine how wise a bulk investment in these would be. Imagine if you could get a week out of a pair! Then if someone bought a thousand of them, they'd have carbon arc for quite a while!
Offered by Brian.
Carbon arc rods with copper coating around them are also available though local welding supply houses.
Offered by Mike.