ess350i, a brake hose is just like any other hydraulic line that is use in any industrial machinery. you can have them custom made with a sample for measurement. but our original bmw brake hose is already steel braided ler, i found out when i cut my e60 520 hose in two, even the aftermarket ones are made with the same hose but with an extra metal weave outside which to me is for aesthetic reason only. the i.d. of most aftermarket hose is smaller, that's why you have a harder brake feel when you use them.
i was looking for them as well for my 520 however nobody has them for e60. but lucky me a forumer here who works in the oil&gas industry know someone that can custom make them. price is 300 only for the pair but you have to wait for a week la. very good quality also.