I got mine from ebay and they are very good (8mm silicone) but I can't see them advertised right now. HotWires by Lemark are very good and you buy those individually so you get the exact sizes you need. I used to have those on the 131 and they were fine and they are now still in use on my Trevi

For the Gamma I got Bosch 8mm leads from a local garage (my usual MOT test centre in fact). Once again they had a selection of different lengths and I bought the lengths I needed. Good leads are important on the Gamma because two of them are about 10cm long and the other two are about 100cm long!