HMAC Key Sizes for MD5, SHA1, SHA224|256|384|512
I'm trying to find an authoritative source for the HMAC Key sizes for each of the hashing algorithms below


Good question.  It turns out that TLS always uses the same length of key as the hash function length (so HMAC-SHA384 would use a 48 byte key).

However, I also can't find any RFC which actually states this.  Neither RFC5246 (which acknowledges HMAC-SHA384 and HMAC-SHA512 as potential MAC algorithms, but doesn't define any ciphersuites that use them) nor RFC5289 (the earliest RFC I can find which actually does define a ciphersuite with HMAC-SHA384 as a MAC algorithm) actually address it.

I suspect that's just something that fell through the cracks; RFC5246 only defined it for those MACs which were actually defined ciphersuites at that time; the author of RFC5289 apparently overlooked the issue.