John McWhorter, a Columbia U linguistics professor who hosts the excellent "Lexicon Valley" podcast, has on several occasions used the phrase a such thing where I would have said such a thing. I thought it odd enough to check Google Ngrams, which shows only one instance in print since the 1800s.
But it occurred to me that we routinely say "no such thing" or "any such thing", so "a such thing" isn't unreasonable. Is this a usage that's coming into vogue? If this were anyone else I'd just say he's mistaken, but I respect him and his credentials enough to doubt myself.