I think they probably did a fair amount. There's footage of all of them in Japan at a conference which was used often in documentaries and videos, and I have a picture of the four of them doing a conference for 'Hot Space' in a book.
There is a wonderful audio interview with all 4 which was done in 1989 on BBC radio for 'The Miracle'. It was released unedited on the U.S. CD 'Queen Talks' included with 'The Queen Collection' (1992). It runs about 54 minutes.
Maybe that would be a good thing to share. I could do it at the same quality as the Rockline show (mono and low bitrate, but perfectly listenable).
Check out 'Sharing The Music' later today. I'll try to make this available.