In Mordor, who created the swords for the Nazgûl?
As they were kings of men from different places before the became wraiths I'd say that their swords were made by men, but I am not sure.
I'm willing to be corrected on this, but I think the answer is "we don't know". The swords could have been made in Mordor, Minas Morgul, Dol Guldur, ... They might even be artifacts from the Nazgul's countries of origin.
The only information I can recall about their weapons is that the blade the Witch King uses to stab Frodo is referred to as a "Morgul knife" by Gandalf in Many Meetings. So this was probably made in Minas Morgul, but it wasn't the Witch King's sword, only a knife that he used with his other hand.
According to lotr fandom, the swords were made in Mordor specifically for the Nazgul.
The Ringwraith sword were long swords of black steel that were hand-forged in Mordor for the Ringwraiths, the deadliest servants of Sauron.
They wielded these weapons mainly during the War of the Ring until their deaths in March 25, 3019, when Sauron was finally destroyed.