The Heil hyd unit that was on my Cletrac was only rated at 200 normal operating psi and 500 max op psi, I thought thats really low!

bearing are the easy bit any bearing shop should be able to match em by size.
the thrust plate is a bit harder. thats a custom machining job. if you knew what the wear limits were it could be reverse engineered ie new is this thick worn out is this thin.
seals are like bearings if you know what size in od depth and bore along with style and material so is it a double lip nbr seal for instance you can replace them.

commercial hydraulics is now part of the parker hannifin group. and they still do the d series pumps. yes you might be better off replacing the pump with a later model unit. the factory cat rams were designed for 1000psi working pressure. relief valve set to 1200psi the type 44 hydro units did a flow of 29 to 40 gph depending on the cartridge fitted.