Searching on Google, I found plenty white LED lights such as this one. The problem might be that color is not a good criteria for selecting bike lights. The most important factors being reliability, light output, and battery life. You should first choose a light that meets those criteria before worrying about color. Most of the high end stuff I see is either black or silver. Perhaps silver could be a good compromise.
As far as seat posts go. Just go a Google Image Search for white seat post and you'll find many different models from high quality manufacturers. For brake levers, are you asking about drop bar levers or interrupter levers? You can get replacement brake hoods in white, but I don't think I've seen any drop bar or interrupter levers that are white. Here again, you may want to use silver as a compromise.
The other option being get unpainted aluminium and paint it yourself. I'm not sure how good of a result this would get.