"...and not all of the ballads HAVE extant tunes."

Indeed not; a fair few have little or no history as 'traditional songs' in the way most of us would understand the term. On the other hand, some of them occur in scores of different versions, each with its own distinct tune, which is why to transcribe Bronson would be such an intimidating task. As Bill D said, it all depends on what the questioner actually needs.

Incidentally, I was one of those who purchased a full set of Bronson from Folkiedave, and I am indeed delighted with it - even though it took the sale of some rare books of my own to raise what knowledgable friends have told me was a very fair asking price.