tractor supply sells some universal hydraulic oil that meets the JDM J20C spec, but not the JDM J20D spec. from the manual, it appears that the J20D is low vis hy-gard and J20C is regular hy-gard.
my manual says i can use either spec (4300) but i have just been using the low vis hy-gard. it's about 2x as expensive as the universal stuff, but it doesn't get changed all that often...except for all the times i've had to re-fill the front axle after repairing all of the problems i've had with it!