In "Glorious Five Year Plan" (S4E04), what appears to be a Beretta 92FS is seen in a police officer's holster seen while filming a television commercial.
Browning Hi-Power
A young Grace Mallory (Sarah Swire) carries what appears to be a Browning Hi-Power during a flashback to 1986 in "Barbary Coast" (S3E03).
Billy Butcher (Karl Urban) carries what appears to be a Colt M1911A1 pistol while attending a gun show in "The Only Man In The Sky" (S3E02).
TBA
Rifles/Carbines
AK-74
Sandanista and Russian troops attacking Soldier Boy (Jensen Ackles) and Billy Butcher (Karl Urban) are armed with AK-74.
Mk 18 Mod 0
What appears to be a Mk 18 Mod 0 lies near a Contra rebel during a flashback to 1986, which would make it's appearance highly anachronistic as the Mk 18 was not produced until 2000 at the earliest. In the present, a Vought SWAT officer is also armed with what appears to be a Mk 18 Mod 0.
Machine Guns
M2 Browning
Gunpowder fires a Browning M2 .50 BMG, mounted on a jeep in "Barbary Coast" (S3E03).
Launchers
Carl Gustaf M2
What appears to be a Swedish Carl Gustaf M2 rocket launcher is seen wielded by Soldier Boy (Jensen Ackles) during the 1980s in "Barbary Coast" (S3E03).
M252 Mortar
What appears to be an M252 Mortar is among the weapons seen in the contra camp in "Barbary Coast" (S3E03).