The most reliable place for Wii and GameCube games is MarioCube (just Google it).
Hit the Get Wii, Wii U, GC, and DS games button.
Join the Google group
Close the groups.google.com page
Go to https://drive.google.com
Use the search bar to find whatever game you want.
When downloading/searching for Wii retail disc games from MarioCube, their file type can be in .wbfs, .rvz, or nkit.gcz. If you plan on using the game on a physical Wii, you should stick to downloading games in .wbfs.
You may notice games that use Nintendo WFC have a Wiimmfi patched version. This is to restore online services. Feel free to download that version.
If they are .zip file type, do not download them. Those are for a different console.
The easiest way to install a .wbfs to a FAT32 formatted SD or USB drive is using Wii Backup Manager. It can transfer the game, split the file if it is larger than 4gb, and create the necessary folder structure all in just a couple button presses.
You can find a guide to downloading and using Wii backup Manager here:
https://wii.guide/wiibackupmanager
There is also a supplemental video guide in case you are having trouble: