I can measure some of the ones I have and send you the dimension and you could probably find some at Grainger or McMaster Carr
I just rebuilt 2 of my pumps, to get the flow/pressure up, I replaced the factory 17 mil gasket with a 2 mil kapton gasket I made from a sheet I purchased. Due to wear, the original gasket is way too thick and cant produce the pressure/flow you will need. have some pic's I took of my disassembly, gasket ant flow testing. email me at rjmc1967@yahoo.com if you would like a copy
ron1967