I've just come across this website called Tju:nbuk which "aims to provide an easy to use repository of public domain tunes. You can search for tunes, view the sheet music, hear the tune and add them to your own collection, or tunebook.".

They (though it's not obvious who they are) claim to have 373 tunes in 14 tunebooks - though I can only count 10 - including 7 of the Lewes Arms tunebooks.

You can search by Time signature, Key signature and/or Rhythm.

A very useful resource, if a little mysterious. Does anyone know more about this?