There is a good Leadbelly book with lyrics, piano score and tab at this site . However, be warned that Leadbelly used very heavy strings and tuned down a fourth from "standard" tuning (so his lowest bass string was tuned to "B" instead of "E"). Nonetheless, if you follow the tab and tune your guitar normally the guitar part will work out OK. You might have to use a capo to get the songs in your voice range.

The book is called "Lead Belly, no stranger to the blues" transcribed by Harry Lewman. It does have "Where Did You Sleep Last Night" and even one of Leadbelly's best versions of "Goodnight Irene".

For Sonny Terry and Brownie McGhee, a lot of folk music collections have some of their things. Look at Homespun Tapes for a start.

Murray