According to the wikia page, "It is available instantly to users that pre-ordered the Tier 1/Limited Edition of the game". How do you get it if you haven't pre-ordered the Limited Edition and it's no longer available?
According to this official EA blog post/press release (emphasis mine):
In addition to exclusive access to this gun, the limited edition also unlocks other weapons without having to rank up first (specifically the TOZ-194 and 870MC2 shotguns).
Other resources, including this guide seem to confirm that the only way to-date to unlock this weapon in multiplayer is to have purchased the limited edition.
For most people, this means the gun is inaccessible in multiplayer.