Try these guys:
CNC, Inc. - Manufacturers of Quality Pedals and Brake Components
They made the master/slave cylinders that were on my car.
I got a rebuild kit for pretty cheap. But if yours are not sleeved you should upgrade to the sleeved cylinders.
Also, the common reason for a master/slave to fail is due to misaligned linkages. It makes an unlined cylinder fail much sooner.