Dear Dan,
The best I can tell, Paul Trevillion is still very much alive and living in England. As recently as 2000, he was illustrating a book about wrestling. He is very prominent in soccer as an illustrator and perhaps also as a photographer. In golf, he has written a book about the 1969 Ryder Cup, his Perfect Putting Method (reissued as Missing Impossible, with tape and DVD), and Save Strokes Like the Stars. He has done illustrations for golf books by Gary Player and Peter Allis.
Here are some references to him online:
Author is Paul Trevillion -- 16 matching titles
PERFECT PUTTING METHOD
Trevillion, Paul
Missing Impossible: Trevillion's Method of Perfect Putting.
Dead Heat: The '69 Ryder Cup Classic
Paul Trevillion
Hardcover, January 1969
DVDs starring Paul Trevillion
Missing Impossible (DVD)
Amazon.com: Books: Save Strokes Like the Stars.
His book publisher is Viking Penguin, and his DVD is distributed by Pegasus. He was formerly artist for the UK soccer comic Roy of the Rovers, and they may have his current address:
Roy of the Rovers.com
Let me know if you need more help tracking him down.
Cheers!
Geoff Mangum
Putting Theorist and Instructor
PuttingZone.com
Golf's most advanced putting instruction