To get them you need to set the "useExternalJSONFilesSpawning" option to "true" in the config. It will then generate a "pixelmon" folder in the base directory (parallel to folders like "mods", "config", "logs", etc) that has all spawning files in their default settings. Edit those and apply the changes either by restarting the game/server or by using "/pokereload" ingame. You can use the "/checkspawns" command to see the resulting spawn rates.
We are using location types and biome categories in our spawn files. If you want to customize (or just check out) those, activate the "useBetterSpawnerConfig" option as well. That will generate the BetterSpawnerConfig.json file under "config/pixelmon".
If you have questions about this it would be easiest for you to join our Discord server and ask in the "#spawner-support" channel.