Unless you’re a collector this may be a game you’ve never played as it was an extremely rare find for the SNES. As usual lately, this is a New Nintendo 3DS release… so if you haven’t kept up with their hardware upgrades, you might be out of luck sadly.
If you do have the New 3DS, go get it here :
http://www.nintendo.com/games/detail/mega-man-x3-3ds