De-chroming requires hardcore processes. It's good enough to just sand really well or sandblast to roughen the surface, then paint with self-etching primer, then prime/paint as usual.
For black painted OEM Mexican handles, try
www.chrisvolkswagen.com. I've got Mexican build parts from them in the past, but you still have to blast, etch, etc to color match, so stick with your german stuff - it's made better.
If you repaint, be sure to remove the tumbler from the door handles before blasting/painting -- easier to keep clean. Wrap it in tape immediately after removal to keep the little slide thingys from falling out and messing up your keyage (been there...). It's a simple puzzle to fix, but you'd rather be doing your GL than puzzles, right?