I just got the Badger Teemo skin. Is this rare?

Not really.

While you can't buy it any longer, it was bought quite often when it was available and then later when the legacy skins resurfaced for limited time. I mean, it was rather cheap (520 RP, so while on sale it was only 260 RP) and it looks okay. I have it too.

It might be rare in a few years though, if those skins won't become available again.

Yeah, I got Ragdoll Poppy, which is decently rare, so i'm happy.