Are there any documented references to where Korob and Sylvia from the Original Series episode, "Catspaw", were from? Did the Federation have mutually-beneficial future contact with the species the Enterprise encountered on Pyris VII?
They were from another galaxy. That much was in the episode.
Digging around on Memory Alpha and Memory Beta gives me a page on the ornithoid life form, which includes these notes:
Two Ornithoid explorers, Korob and Silvia, set up an observation outpost on Pyris VII in the 23rd century. They encountered the USS Enterprise and held members of the crew for study in 2267. Both died after James T. Kirk destroyed their means of support in an effort to escape capture. (TOS: "Catspaw")
In the 24th century, information about the Ornithoids were used in schools as teaching aids in comparative xenobiology lessons. (DS9: "A Man Alone", "The Nagus")
In 2369 Jake Sisko was working on his homework on a PADD that featured two drawings of the Ornithoid lifeform. (DS9: "If Wishes Were Horses")
Later that year, a Bajoran student also had a PADD with drawings of the lifeform on his desk, which also featured a computer monitor with similar drawings. (DS9: "In the Hands of the Prophets")
However, these are only notes for xenobiology, which could have been learned from research on their bodies after Korob and Silvia died at the end of the episode.
Because they were 1) from another galaxy, 2) unable to contact their people before they died, I doubt the Federation ever managed to make contact, and their people could have simply deemed our galaxy too dangerous to return to without more preparation.