The query implies the intent to download the game without purchase ("free"). It is critical to note the legal status of such actions:

For those who found the original NES games too brutal, this entry added an accessible mode without sacrificing the core gameplay. How to Play Mega Man 10 Today

Although the Wii Shop Channel and Wii U eShop are no longer accessible, archived versions of these stores provide a way to re-download purchased games. If you previously purchased Mega Man 10, you might still be able to access it.