I've been looking for one for awhile. PSA has one McCartney (64 B&W) listed in their population report, so there's that and I'd imagine there is a small number of blue flips as well. Ringo just quit signing through the mail in the past 5-6 years so I'd imagine he's got a handful out there.
My wife and I got backstage and VIP tickets for a McCartney show in 2011 and I put one in my jacket pocket just in case, but I honestly figured that I would never get within 20 feet of him and in reality never actually saw him back stage. (Drummer was super cool though, can't remember his name - bigger guy.) At the same show there was a friend of a friend who got on stage during the show by bringing a sign begging him to sign her tattoo. It probably helped that she is an attractive young female, but taking a "Macca sign my Topps Card!" sign to a show might not hurt!
Pic my wife took at the show:
On the way to tattoo his signature after the show:
