You can create your own maps using J.A.C.K or VHE (Valve Hammer Editor) to theme it about Pokemon (using custom WADs themed of that, or creating your own textures using Wally), or else, you can search for any map at modding platforms like GameBanana and modify it as you wish.
There's one map example by Mamorex, which contains a zip with decompiled map files inside that you can use for create your own version of that map, or just to grab the textures (inside the WAD file) to use it and make your Pokemon themed map:
https://gamebanana.com/mods/987.