1. Musicnotes: You can purchase and download the piano/vocal/guitar and guitar tab arrangements of Montgomery Gentry song from MusicNotes Website.
2. Hal Leonard is another leading publisher of sheet music and songbooks. Musicnotes Website sells a variety of Montgomery's arrangements and songbooks and you can purchase directly from them.
3. Amazon also offers a wide selection of sheet music and songbooks, sometimes at the best discounted prices from Hal Leonard and sometimes other sources. It might be worth checking there or searching online music stores of your preference too.