I wanted to finally contribute something meaningful to the community so here is my own custom Pokemon BW Tileset. I originally designed it for use in my gamePokemon Adventure however, I am no longer going to use it in my game as I'm changing the format slightly so they are not needed.
As you can see, it contains the basic tiles of a Pokemon tileset in the standard 16x16 pixel size. You might need to adjust it to make it usable in RMXP, I don't really know as I use Game Maker.
For anyone who is curious, I made the tileset by playing the games and basing the tiles on screen shots I took.
These tiles are available for community use but CREDIT IS REQUIRED.
Here is an example of a town I made using these tiles & some others: