Hi mark59, The Classicals have the widest necks, it's a bit harder to find steel strings with wide necks but this guitar has
Seagull S6+ Folk
it has a smaller body but is based on a classical guitar, if you've got loads of cash you could try a Larrivee Jumbo or alternatively you could get a custom neck done for you as far as I know Taylor guitars offer this service, I have my twelve string strung as a 6 string at the moment might offend the purists but it hasn't harmed my guitar and I have loads of fretboard space.
Cheers
Chris
You don't stop laughing when you grow old; you grow old when you stop laughing.