IDK about just that grille but you can get a black set (upper and lower) here:
Not painted or body-color but if you're into the black look on a non-black van, it breaks up the monochrome nicely. On a black van, you would barely notice a difference I bet between painted black and unpainted black.
If you want body-color (and to just replace the lower one) you might have to go to VW directly and get a primed one, have it painted, etc. That'll cost probably at least the $150 for the set of black ones I'm sure.
The grilles are just screwed in IIRC but I think you might have to remove the upper one to get to the lower one and IIRC the lower one might not come out w/o removing the entire lower grille panel (but I could be wrong on that). However it's not that hard to remove the entire grille panel either.
1. Remove upper grille. It's two screws atop the radiator support (very evident) and one allen key (I think) bolt that is through the "crotch" of the VW emblem.
2. Remove the turn signals. Reach in each corner under the hood and remove the spring hook and slide the lamps out. You can leave them dangling by the wires.
3. Remove one screw each side now exposed by the absent signals.
4. Remove three screws in the lower grille (one each end and one center).
5. Unsnap the entire metal lower panel with the lower grille in it. It just clips to the fenders. Just be careful to not scratch your bumper. They're kinda grippy though.
6. With that off, you probably can get the lower grille out of the lower panel now (I never had to go that far but IIRC there was nothing that I remember to get the lower grille out of the lower panel while the panel was still on the car (maybe I'm wrong?) so that's why you have to remove the lower panel.)
Assembly is reverse of removal.