i advise you go to myspace, go to the music directory and search through the entire bluegrass genre. there's a lot of crap but among it i'm sure you'll find something you're looking for. just take scraps from songs here and there that will fit together stylistically. i won't tell anyone.
isn't there that one song from super mario world that sounds really bluegrass, with a banjo and all? maybe just remix that one, that'll be sweet (i'd listen to it fosh).