Hey there rling. I personaly haven't seen any Whites in The Channel Islands, though I'm sure they are around. All the GWS I've had the excitment of seeing were up in central California. Quite the humbling sight. I'm sure you have a tale or two from your side of the Pacific.
Unfortunately we seem to have killed most of ours late last century :-( I believe you need a multi-day trip out of SA to have much chance of seeing one. Though if you believe the media here, they're everywhere... wobbegongs and little whalers mysteriously turn into GWS every day! ;-)
The closest I got to one was in South Africa, off Gansbaai. In case you didn't know: the top side is kinda rough like sandpaper, but the underneath is quite smooth.

Cheers
R