A major on-line resource for the type of thing you're looking for is The Ballad Index. http://www.csufresno.edu/folklore/BalladIndexTOC.html (sorry no blue clicky but no angle brackets either). Lots of information there and always a good starting point for your own research.

I find that the program at most camps varies depending on who the staff people are. Vocal week at Augusta Heritage in Elkins WV might be a good possibility, but check who's there first. The same goes for Common Ground, which to me seems to have more of an emphasis on instruments and songwriting than traditional music.

Don't overlook Folk Music Week at Pinewoods Camp (near Plymouth MA) of the Country Dance & Song Society. Sara Grey was program chair for the last couple of years, and brought traditional ballad-singers over from Scotland and Ireland, as well as from the US. Over the years they've had a huge range of teachers and they've always had a strong emphasis on traditional song. Check out their programs at http://www.cdss.org/ Their website lists their programs for the past few years. With an interest in traditional singing that's the place I'd check out first. Unfortunately I'll not be there this year but I've been many times in the past.