good job man! keep 'em coming you've got a good sense of balance on writing for the instrument.
on getting publishing rights, hmm you'd prob need to contact the since the composer and depending on contracts the studio would probably need to get in on any and all royalties.
you could probably get a non commercial copyright easier and put the music out for free but at least make sure you get credit as the arranger in any public performances again, it might be as easy and going to legal zoom and filling out a form or something