Do you really truly want authenticity? Are you really brave and dedicated?
Then I'll tell you - though I can't guarantee they're still available.
Before he died Peter Kennedy was selling recordings on Folktrax that Jimmy Carpenter made in Britain between the wars. For those of you who don't know, Carpenter was an American academic who was given a trip to England by his University to collect old ballads that might still be in oral tradition. The story goes that at a very early stage he wound up in a pub getting drunk with some old sailors who didn't know any ballads but gave him some shanties, and that's what he did till his money ran out!
Now for the bad bit. The recordings are almost (but I assure you not quite) unlistenable toable. Many sound as if the singer had his head in a bucket, whilst frying sausages on the platform of Euston Station.
But you said you were brave, dedicated and wanted true authenticity!
I've learn a lot from them. You may too.