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.
If we presume "Morgul" as the term used to be linked with Minas Morgul, which thus implies a domain / stronghold of Sauron, then we can look to early drafts of The Fellowship of the Ring:
Gandalf calls the weapon that was used 'a deadly blade, the knife of the Necromancer which remains in the wound', not a 'Morgul-knife'
In a later draft:
The 'Morgul-knife' is still the 'knife of the Necromancer'
Thus - we can see that originally, Tolkien was associating the one named weapon in the text very directly with Sauron. He later changed it of course to 'Morgul-knife' but again, given the association of Minas Morgul and Sauron, it isn't unreasonable to presume then that Sauron or someone quite close to him constructed their weapons.
Source: The Return of the Shadow: The History of the Lord of the Rings, Pt1 - Christopher Tolkien
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.