BMW used to sell kits to do that, but they are no longer listed anywhere I can find them. You have a two stage problem - the first part is to find a matching caliper and the second is a master cylinder.
The best way to buy Brembo F08 calipers would be to buy a pair from somewhere like desmo heaven, remembering that what they call a "left" caliper" will be out "right" and vice versa. The size master cylinder you buy will be dependant on what size bores are in the F08s you buy = 36,38 or 40mm.
The last problem is plumbing, you have options - a short hose from master cylinder to splitter (if you don't have one they are readily available), or you may choose to run a single long hose to one of the calipers and then remove that caliper's bleeder and run a short hose to the second caliper (I don't like this method as i think it is visually unappealing).
other alternatives are:-
Buy a set of F08s from an early model K series and then machine the mounting "ears" so that the calipers centre over the disc. Noting that the work involved in this you may as well buy 4 spot calipers and machine them to fit.
Disc wise I am not able to locate anyone still making Cast Iron rotor replacements so you will be buying new Grimecia/Brembo ones form Motobins or Boxer works - taking a deep breath for Speigler.
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Out of curiosity, are you going to leave the gearing the same? With the extra power from the 860 kit you could fit a 32:10 or even 32:11 final drive (at the cost of having to mentally adjust the indicated speed on the speedo unless you want to go GPS speedo).
Which 860 kit did you buy?
