However, where they come from is a different matter - they actually come from a different dimension.
We could have so, every once in a while in a rare chance a portal opens in the sky - you can't go through, it'd just be a texture. Then, different Unown would spawn near it.
Or, including what I just said, a method of building/summoning the Unown in a special way, unnatural, such as finding blocks called "Unown Ruins Piece" or something, and when mined drops an "Unown Artifact", which then when something is done with, summons that portal.
Ima post this in the Suggest a Feature thread