There is a list of songs collected by RVW in an appendix to Michael Kennedy, The Works of Ralph Vaughan Williams, OUP 1964. It doesn't include material noted in collaboration with Ella M Leather (who also sent him cylinders for transcription), or songs originally noted by George Gardiner and Charles Gamblin, some of which RVW re-transcribed with the aid of recordings, but it does cover all the material in the MS collection, with dates and locations. I have a copy somewhere but I couldn't find it the other day.

Most of the cylinder recordings are lost, and those which survive are imperfectly documented. It appears that copies are to be made available online by the Sound Archive of the British Library quite soon:

http://www.collectbritain.co.uk/collections/wax/

There is one to be heard there at present: John Locke of Herefordshire, c.1908, singing Died for Love followed by a hornpipe played on the fiddle. Quite likely recorded by Ella Leather and part of the residual Vaughan Williams material, but I don't know the details.