Actually, most Pokemon do have locations, for example Mienfoo, Golduck, etc. Basically anything that appears in grass or on water.
However, some Pokemon are missing, in particular ones you can only get by evolution (e.g. Gigalith) and several of the legendary Pokemon. This is true for all games, not just BW2, and will be fixed when I can.
If you notice anyone missing from the actual locations page (the pages from here), you can check the Locations guide corrections post and submit a correction, it will be much appreciated.