For the model that I had (since sold it), I used copper-clad gouging electrodes that I bought at a local welding shop. They were 1/4" diameter x 12" long and made by ARCAIR.
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As an alternate, you could always salvage the carbons from smaller lead-acid batteries. Lindsay Publications sold a booklet by Don Meador about doing this, along with other books on building the actual torch and a water resistor for current control. The booklet on carbon rods is available at Amazon:
How to Salvage Carbon Rods from Batteries for Carbon Arcs: Don Meador: Amazon.com: Books
As far as the torches being obsolete, that's a matter of opinion. If you are looking for an inexpensive way to generate massive amounts of heat (for bending, forming or gouging steel, for example), these torches are great. IMHO, they are a bit harder to control for brazing applications.
If you use one of these torches, wear long sleeves and cover any exposed flesh, as you should be doing anyway when welding. The last time I used one of these torches, I wore short sleeves and got a nasty "sunburn" from the extremely bright light generated when the rods touched off.
Hope this helps.