I have been looking around an BBK's as well and have found a couple sites RHDjapan.com and blackhawkjapan.com also there is a company in South Korea called NeoTech who do BBK's and suspension and apparently they do kits for the Alphards and Vellfires but you might need to message them about it. As the brakes on our vehicles are probably used across many other Toyota models you could also try GodSpeed Brakes as i have used them before for my Subaru's and the stuff they have is pretty good. There you can find kits from high end companies like Blitz and Endless Brakes. I had a look at the Blitz package and for about £1300 you get the calipers, discs, pads, hub bracket and braided lines which i thought was pretty good. Hopefully this is of some use