They are a random CR2 witchcraft scroll, so first make a larger number of random blank witchcraft scrolls (paper/parchment + pixie dust, both of which are plentiful in the game), then use the magic quill & ink on them and you'll turn them into random low-level witchcraft scrolls - with a bit of luck you'll get a few unlock scrolls that way. (Savescum if that's the way you roll.)
Note that CR3+ increases the number of different random witchcraft scroll outcomes from crafting, so it is ideal to craft them with a crafter that has exactly CR2 to maximize the odds of getting the desired outcome. The easiest way to do this is to give a CR0 crafter belt/shoulders with +crafting, if you've got them.
It is very pleasant to unlock the Armoury with a stack of unlock scrolls already in one's possession.
