1968 gtx regular power brakes need part number and where can I locate one thanks for master cylinder. or replacement for same.

4 wheel drum or front disc?
The drum brake ones are available both new and rebuilt just about everywhere. Even original Bendix ones aren't that hard to find.
Disc ones are harder to find.

I thought napa or someone was making a 68-70 disc brake master with the lines on the engine side now?

RoackAuto shows Cardone available for a 68 GTX with front discs and engine side outlets, wire bail holding top on. there are a bunch of all drum M/C selections with fender side outlets, bolt on top.

4 wheel drum. part # please

1323 or 10-1323 is a common part number for the 4 wheel drum MC. Raybestos # is MC 36221 or NAPA United is 36221. Raybestos rebuilt is RMC 36221.
I'm sure there are other aftermarket part numbers besides those I've listed.
Or are you seeking an original NOS part? There are a number of Chrysler part numbers used over the 4 model years they used that style, and 2 or 3 casting numbers if you are trying to ID an original.