Welcome to the forum You have come to the right place for collaboration. There have been a number of collaborations among members of this forum over the years. And some excellent music has resulted. I am confident you will find the right person(s).
i think it would be easier if you posted the song so people could listen, then let you know if that would be something that they are capable of doing. also, did you write all the parts and just want help mixing them, or would you like help on writing some of the parts either way, a little more info would be great. thanks.
I guess I'm not to comfortable sharing my songs with everyone. But I'm not agaist sending people some mp3's if they are really interested.
As for the collabration. I have some parts written and some parts that aren't.
For example, written. I have this piano piece that I want to use for the introduction of the album, but I would want someone to change it and rearrange it so that it will be a violin solo accompanied by the string section.
And for the unwritten parts, I may just have a track with a guitar and a vocal, were the collaborator can freely compose the string sections based on the mood of the song.