http://www.gbfans.com/ghostbusters/books/piano-sheet-music/2/There is the sheet music on GBfans. hopefully that can be some help. (^_^) It has the chords though the part that really makes it fun to play is all the little lead bits. Most of them probably aren't too hard to figure out noodling around.
The GB theme on NES is pretty much based on the sheet music if that says anything with the exception of it couldn't handle all the notes I guess. It does it's best to be pretty basic and straightforward.
I'd like to see an elaborate tab of it though. It's fun trying to replicate the opening guitar of the theme trying to sound ghostly… I play it on the A string starting on the 2nd fret(B) and slide quickly up and down an octave to the 14th fret and back. That sounds decent to me. (*winston)