Singer John Mayer is reportedly planning to buy a rare watch as a Christmas gift for his girlfriend and pop star Katy Perry. The 36-year-old has taken help of an antiques dealer to buy the timepiece, reports contactmusic.com. ‘He's asked a friend who's a rare watch dealer to email him photos of options. John's a great giver, who finds unique presents,’ a source said. Mayer will have to go a long way to beat last year's gift, when he got her a custom designed guitar.