Secret Weapon

Was reading some mission guides, when i came across some notes about "secret" weapons. They seem to be modified and more handy and more user friendly, from what i read, there are 6 secret weapons and one hidden and known to be never found.
Toxin Blade (combat knife)
Red Greasel Hunter (pistol)
Hellfire Boltcaster (boltcaster)
Assassin Pistol (pistol)
Dragon Tooth Sword (resurrection from old DX)
Widowmaker SMG (SMG)
hidden but believed to exist
Gunther Hermann's so called "Skull Gun" that was mentioned earlier from the old DX in his computer account when he has an email, mentioning about an import of a new weapon called a Skull Gun. It also happens in DX:IW, that the receipt mentioned that Sam Carter (i think before he was dismissed) received this gun, but was forced to send it back to the manufacturers because JC killed Gunther. It appears that the gun was made and still to be around somewhere, but dunno where to look first since it left no clue on the original manufacturing place.
i kno that there is one created in DXMP (and is very crummy), but i want to see the real one and kno its potential powers if Gunther wanted it so much.
Toxin Blade (combat knife)
Red Greasel Hunter (pistol)
Hellfire Boltcaster (boltcaster)
Assassin Pistol (pistol)
Dragon Tooth Sword (resurrection from old DX)
Widowmaker SMG (SMG)
hidden but believed to exist
Gunther Hermann's so called "Skull Gun" that was mentioned earlier from the old DX in his computer account when he has an email, mentioning about an import of a new weapon called a Skull Gun. It also happens in DX:IW, that the receipt mentioned that Sam Carter (i think before he was dismissed) received this gun, but was forced to send it back to the manufacturers because JC killed Gunther. It appears that the gun was made and still to be around somewhere, but dunno where to look first since it left no clue on the original manufacturing place.
i kno that there is one created in DXMP (and is very crummy), but i want to see the real one and kno its potential powers if Gunther wanted it so much.