Johnson Matthey is the only one I have experience of, and only rods. Ablemable has different thickness of rods, at least last time I ordered. There's not too much difference, except price, between Silverflo 55 and 452 (45% silver). Silverflo 30 is a good filler, but needs a little more heat, not much. You can buy various tube straighteners, some very expensive, some a few quid. Kunifer, I always think has a kind of memory, so is difficult to get really straight and is just a tad soft, but works. Someone did post a supplier, but I can't find it now, gas pipe maybe?