This item does not fit into the loot paradigm of D&D 5e particularly well.
5e magic items outside of cheap consumables like healing potions are generally things that break the bounded accuracy of the game by providing a +1 (up to the limit of 3 attuned items) or more bonus to [something], or they provide an asymmetric benefit of some kind of which is very meaningful within the niche that it sits in (like a Broom of Flying). The odd stuff printed in addition to this can often not be very meaningful for an adventuring party or in a few cases wildly overpowered.
This item instead provides a small bonus which is nice but not great. For the average Rogue, going from 10 str to 11 str isn't a big deal. If they have an odd score below 13 to use it on, they get a +1 on.. things they aren't specialized in. 5e very much rewards specialization especially in terms of ability scores - PCs with low Con are basically nonexistent, as an example. And the one time I took low con, i've been knocked unconscious by passing breezes and basically sat out several combats. However 5e also lets people get by with using mostly their high scores very easily - a guy with a 3 in strength can go multiple sessions without needing to roll it, and that's with a DM actively asking for athletics rolls, and that's if the guy has no-one willing to carry his weak ass and no ability to teleport.
So to reiterate - this doesn't push bounded accuracy (increasing a low stat does not do that), doesn't provide an asymmetric benefit, and yet you wouldn't want it to be as common as healing potions (everyone getting every stat lower than 13 to 13 removes character design choices and is very samey). It's too weak for higher grades of magic item, and it's not a great choice to be common as muck.
Ergo, treat it like an adventure-specific magic item. There's one. Maybe 2. Total. If they show up in loot, they're a Common item, they can show up at any level and they don't count as or replace a Broom of Flying. But you don't get them twice. Or at least, not three times. It comes up, it's neat, and then it's gone is the place it best sits at in the game, like in the temple of the ice queen there's an ice rune that lets you shoot ice from your nostrils or whatever. It's not really factored into the expected magic items of the game, and that's fine, you just now have a PC that can shoot ice from their nostrils (or have a 12 dex instead of 11, w/e).