Sponginess could be a bunch of things. But yes, non-ABS R32 (it may also have to be turbo) master fits and gives you a bigger bore. BM44 rings a bell for the part number, but it's been a few years so you best Google it and check.
Also check what you should do with your bias valve given your rear brakes so your front-rear balance is good.
As for finding them, check skylines australia for people wrecking cars, or specialist wreckers.