Body kits are basically just cosmetic. Larger air intakes are usually good for brake cooling (if they are really functional), and in theory the spoilers do affect air drag, but not by much to be honest.
Your options are teh usual suspects:
- BMW M Tech
- AC Schnitzer
Google for pictures. It really is up to your taste.
It is extremely rar to find them prepainted. You will most likely be facing shipping costs, as well as paint shop xpenses.