Because the Wii Shop Channel is discontinued, you can no longer purchase digital copies directly from Nintendo. However, physical discs are widely available on the second-hand market: Often stocks used copies for around $9.99.
That being said, if you're looking for general information on WWE 13 or how to legally obtain a copy, here's some relevant information:
WWE ’13 was notable for shifting the annual franchise’s focus from a general simulation to a specific historical narrative: the WWE Attitude Era (roughly 1997–2002). It featured a single-player mode titled "Attitude Era" that recreated iconic matches and moments. On the Wii, the game differed from its high-definition counterparts (PS3, Xbox 360). It featured lower-resolution textures, different control schemes utilizing the Wii Remote and Nunchuk, and lacked certain online features. Despite these limitations, the Wii version found an audience among younger players and those who preferred motion controls.
If you type into Google, you will find hundreds of forums, torrent sites, and file-hosting links (Megaupload, Rapidgator, etc.). Before clicking, you must understand the legal landscape.
Downloading copyrighted material without permission is illegal. WWE '13 is a copyrighted game, and downloading an ISO of it could infringe on the rights of the game's creators and publishers. Always opt for legal purchases or free, officially distributed content.