Here is a possible contact for Jon Raven's family. Mike was Jon's brother.

Subject: RE: Joan Mills, folk singer with Mike Raven
From: GUEST,Malc Love
Date: 11 Jun 12 - 05:02 AM

Re the recordings of Joan Mills and Mike Raven.There are details on the website,however if you have problems I hold a complete stock of their work.
Details
Malc Love
10 Holmes Orchard
Alveley,Bridgnorth ,Shropshire,
WV15 6NX
Tel 07890 068135
Home 01746 780547