@Ac3z-i found this about AA12 with a HB sensor in singleplayer
In the Spec Ops mission, Acceptable Losses, players start off with the AA-12 with three different attachments, the Red Dot Sight, Silencer and a Heartbeat Sensor. This is impossible in multiplayer.
And this is for the camo:
It is possible to find a Woodland camouflage Striker when the enemy deploys smoke screens on "Loose Ends", as a matter of fact, it can be very rarely found in the other camos in "The Enemy Of My Enemy".
There are alot of these facts in cod wikia