I've done my research and here is the full list of pump shotguns in the game:
ITA12L (Jackal/Mira)
ITA12S (Jackal/Mira)
M590A1 (Sledge/Thatcher/Smoke/Mute/Warden)
M870 (Jager/Bandit)
SG-CQB (Twitch/Doc/Rook/Lion)
SuperNova (Hibana/Echo/Amaru)
Super Shorty (Castle/Gridlock)
Standard chill scrim but you can only use those guns listed.
Event will START at the listed time
EU Members have priority place for this event, NA members will be chosen afterwards to fill the spaces so sign up if you would like to participate!