Are there any Hitotsui Hajime songs that I can listen to? A Certain Scientific Railgun, Toaru Kagaku no Rērugan.

During The Scientific Railgun Anime and Manga series you see the girls like Ruiko Saten and Kazari Uiharu listening to music from Hitotsui Hajime on their mobile cellphones. I wanted to know if this is an actual Japanese band or music I can listen to. Like an OST Soundtrack or something? Does the music even exist? Or is it just something designed for the Anime only? Thank you for all the help in advance. This is what I'm talking about. https://images.app.goo.gl/HLR84ha2oMaBhAY18