It's not magical, but the Svartálfar is also made Sif's hair.
From Wikipedia:Faulkes' translation1 (via https://en.wikipedia.org/wiki/Sk%C3%AD%C3%B0bla%C3%B0nirWikipedia):
In chapter 96, a myth explaining Skíðblaðnir's creation is provided. The chapter details that the god Loki once cut off the goddess's Sif's hair in an act of mischief. Sif's husband, Thor, enraged, found Loki, caught hold of him, and threatened to break every last bone in his body. Loki promises to have the Svartálfar make Sif a new head of hair that will grow just as any other. Loki goes to the dwarfs known as Ivaldi's sons, and they made not only Sif a new head of gold hair but also Skíðblaðnir and the spear Gungnir.
In chapter 96, a myth explaining Skíðblaðnir's creation is provided. The chapter details that the god Loki once cut off the goddess's Sif's hair in an act of mischief. Sif's husband, Thor, enraged, found Loki, caught hold of him, and threatened to break every last bone in his body. Loki promises to have the Svartálfar make Sif a new head of hair that will grow just as any other. Loki goes to the dwarfs known as Ivaldi's sons, and they made not only Sif a new head of gold hair but also Skíðblaðnir and the spear Gungnir.
[6]1 Faulkes, Anthony (Trans.) (1995). Edda. Everyman. ISBN 0-460-87616-3. Chapters 96-97.
