The long brake cables and even the throttle cables are a trike problem. I bought all the parts from Flanders Motorcycle Supply in California. I started buying from them in 1972. With any long cables it's always best to buy nylon lined housing . Buying in bulk is not what a lot of people want to do but if you don't get it right the first time it is a waisted effort. I start with the wire size for clutch & Brake I bought ( .08 ) diameter wire that is a 1 X19 strand their part # 610-03120 and I bought housing a Rectangular chrome steel core with nylon liner with abrasion resistant plastic outer cover O.D. .233 I.D. .098 for use with the wire above. This housing part # 610-03325. The parts for the ends of the housing is # 620-20330 large clutch ferrule for the wire. The parts for the brake lever end you will have to measure and look at their catalog for the proper fittings for your levers.
For the throttle cable I bought their part # 610-03100 wire that is .064 diameter and also a 1X19 strand.
And the Conduit housing part # 610-03315 with an O.D of .215 and I.D. .086 and a Ferrule for that is housing # 620-20220.
I have made throttle cables for VW trikes that were about 15 feet long.
I am not your average go cheap guy so buying quality parts works for me.
Band brakes are marginal at best but good control cables help a lot.
Steve