I checked with The Compressor Warehouse (an A/C and heating parts wholesaler that can get damned near anything), and while they have new compressors, expansion valves, and condensors for IIs, they have no hoses or evaporators.
You could try taking the evaporator to a radiator shop so they could pressure test it and possibly repair it for you, or Phil's Mustang II Specialty shop may have a good used one.