I would think you have seen these on ebay, but just in case there are some Nikko Steel C-10 rods in 2.5mm 2 Kg Vac Pac for £22 including delivery on Ebay, the label says they are for root runs on pipe work. Item number 221937463562. Some 4mm at £15.50 also on the bay, would not know what they are like to use. But one has a link to a data sheet for reference if it helps. Does not say what voltage is recommended just DCEP.
Adrian
Adrian