In 25 years I have never seen a Quincy oil pump wear out, but I suppose it can happen (I would need some decent photographs to see what the shop considers worn out). I presume it's the older vane style pump which can wear out vanes, groove the oil pump ring, or break tension springs, but all of that should be fixable. I would give the lube system a major going over, since I would think it is a problem elsewhere other than the pump. There are other things that could prevent it from working, like a bad pressure regulator, a missing o-ring on the end of the crankshaft, plugged suction line, wrong rotation for the setting of the oil pump, or an oil pressure bleed valve on the crank that isn't working correctly.
Make sure the ring that the vanes spin inside is properly set for the rotation of the pump. The vanes are supposed to pull the ring to the proper position, but they rarely (never) do, so it is up to the operator to move it to where it should be. I have no idea how well the shop knows Quincys, so they may have done all of this already.
It should not be hard to source used Quincy oil pump parts from a decent compressor shop. The entire end bearing carrier can be swapped out for a newer style with geroter style pump and the spin-on filter if you wanted to. You might need to re-shim the oil seal carrier a few thou to get proper end float on the crank, but that's easy.
