This, so far, is my most popular Youtube video. Also referred to as a Nashville-tuned guitar or "Poor Man's" 12-string, the High-Strung guitar is very fun tool for recording or writing. Basically you string the guitar up with the high six strings from a 12-string set. On my Larivee Parlor guitar I use half of an Elixir 12-string light set. It's still tuned, EADGBE, so you can play it just like a regular guitar, but the bottom four strings are tuned up an octave. You can do this to any guitar, but would I use a cheaper, back-up instrument just to be safe, and you are going to want to leave it tuned that way for ever, trust me. Even basic open chords sound magical on this axe. Seventh chords especially sound very piano like, because the tunings allows for very tight voicings, something that would be very difficult on a normally tuned guitar.
You won't find any one marketing high-strung string sets, although I will talk to Elixir about this, but if just buy an Elixir 12-string Set, you can split it up into two sets, a high strung set and a normal light set.