NHL 09 was released in 2008 for the PlayStation 3, Xbox 360, PlayStation 2, and PC. It is abandonware (no longer sold digitally by EA) and has no official digital storefronts active today. Online servers for multiplayer are also shut down.
Because of this, your method depends entirely on which platform you want to use. Since EA no longer sells NHL 09 on Steam or Origin (now EA App), the only legal-ish way is through abandonware sites that archive old, unsold games. Download NHL 09