If you are looking for a black wood file cabinet, you might have a difficult time finding the right one for your office or home.
Most filing cabinets come in two styles: metal, or wood. It is pretty easy to find black metal filing cabinets, or wood file cabinets that are any one of several colors other than black.
While I'm not sure of the reason, I think it has to do with the fact that most offices that are looking for wooden furniture are actually trying to match a style of wood for the rest of their office, ie: oak, maple, cherry, etc.
There is a really simple solution, though: paint. No, I'm not joking. As long as the wood file cabinet you buy isn't the 'laminate' kind (pressed wood with an imitation wood finish laminated to the outside), you should be ok. Grab a can of Kilz, or other primer that can be used atop a polished finish. Remove all the hardware (knobs, hinges, etc.), prime it, and paint with two coats of black paint, either matte or gloss finish.
If you are really interested in finding a black wood file cabinet, this is a great way to do it. Since almost no one actually sells them already black, it opens up your selection of style that you want. You can get the exact size, shape, edging, hardware, etc., and then just paint it to match. You can have high-quality style that matches your decor perfectly. Try doing that with a metal file cabinet!
So, while you may only find a few links to sites with a black wood file cabinet, it doesn't mean you still can't have one for your office by painting one!