Vehicle Wiring Products in Ilkeston, Notts, supply all sizes of control cables and fittings. They have a website. Do a Google search.
As far as making up cables, it's best to use plumbers solder and Bakers Fluid flux, as it's harder than the more usual cored solder. I've been used to making my own cables for years, but have only recently started using a solder pot, which is MUCH better! I expect you know that the end of the cable needs to be "mushroomed"? If you make your own nipples, make sure that the hole for the cable is a snug fit, rather than oversized.