They are very pricey. I toyed for awhile with the idea of making my own setup, utilizing a clutch master from a late '80's S-10, with the external fluid reservoir, and using a standard dual brake master and booster from a mid/late '80's C-10 to split the system. With a little imagination you can rig some linkage mods for the clutch pedal to get it to work. Very little should have to be done for the brake master.
In the end, I obtained an old Hydro-Vac unit (external booster) and I will use that when I get time to make a mounting bracket and plumb it into the brake line.