My Pokémon Ranch was delisted from the Wii Shop Channel in 2014 and cannot be purchased or downloaded. As a WiiWare title with no physical release, there is no legitimate way to acquire it today.
You can still launch and play the offline portion (viewing Pokémon models, taking snapshots) if the title remains on your Wii's system memory or SD card. Online features are permanently disabled.
For modern Pokémon storage/interaction, use Pokémon HOME on Switch/mobile.