I was curious myself, but not enough to search it out yet, My experience has been extended warranties were sold (at varying prices) by the different OEM dealers, and the likes of Carmax etc ( ignoring the 500 junk calls we all get every month from those other folks ). No clue how they’ll happen with Teslas - but I’d expect them eventually?
Having said that, in the last 3 extended warranties I paid for, only one paid for itself on repairs (Carmax on a Toyota Avalon).