If you know anyone who is a decent machinist you *COULD* buy the brakes piecemeal and build a custom package, but it entails a knowledge of piston sizing and pad area, so you'd need help with the sizing aspects. I usually build my own brake systems to save money, looking out on the race car auction sites for suitable discs and calipers. I found some new Porsche 962 Le Mans car Brembo front calipers, and a pair of used Aston Martin DB9 rear calipers, which I mated to discs I also found on forums or had to hand. I made up suitable brackets and bells and got a nice set up for half of what a commercial package would cost. Pics are dotted around ftp://ftp.chriswilson.tv/skyline_stuff
under various brake headings. I also made the bias brake set up using twin master cylinders.