Hy 52vff, welcome, your master cylinder has a bore of 1 1/4" Raybestos MC9220 at RockAuto $119.67 this is a new master cylinder
at Napa their p/n NMC P9220 $119 this is a remanufactured master cylinder, NMC M9220 $199 this is a new master cylinder. As Grigg said you could disassemble your master cylinder and put a kit in it if the bore is not too pitted, if your brakes work now but you have a leak at the pushrod end of the master cylinder your master cylinder should be rebuildable. as to the Hydrovac Geoff at Alreta should be able to help with parts or a rebuilt unit, hope that helps.
