I've just posted a list of recommended courses/teachers on another thread, some (but not all) of them trad/folk-oriented. I have taken part in all of them, so if you have any queries, just ask. (I've never really used websites or books for actual tuition purposes, so I feel I can't recommend any.) Hope this is helpful.

Here's the link to that other thread:

Link to thread with list of courses/teachers

Nearly all use the master-class format. I strongly recommend this format for learning to sing. It's intense, challenging, but satisfying and successful. And it's the epitome of learning-by-doing, always the best way to learn anything.