I believe you want the Melling K20I oil pump kit. I got this through my machinist. Its a factory replacement, not high volume. I just installed this in my rebuild. It contains new gears, gasket, relief thingy, and a variety of springs.
Of the 4 springs contained in the package not one of them looked exactly identical to the stock spring.
Not wanting to mess around, i put the original 100,000 mile spring back in with the new relief valve (old one was fine). Put the new gears in. After 100,000 miles, there was some wear on the face of the oil pump cover plate. A quick trip to the machine shop removed about 10-20 thou off the face. Now post rebuild I have 35 psi hot idle oil pressure, even considering my main bearing clearances are above the high end of factory spec at 2 thou.