This spelling is found in the Marillion song '
KAYLEIGH'. I found out something of the origin of the song title in a copy of Classic Rock magazine's Top 100 Rock albums (
April 2006) It was an interview with the lead singer, he wrote the song about a break up with his then girlfriend and he just combined her first and last names to create the song title
Kay &
Leigh. Perhaps this spelling is where it originated, the song was written around 1985 i think. after that it seems it became very popular to give your child that name.
Andy.