Chiptune artist here willing to collaborate with you for GBJAM 5! Check out my SoundCloud here: https://soundcloud.com/ccolongames.
I have been making music every week for a while now, and at the same time I've been making Chiptunes for a twin stick shooter, called Mutant Chicken (coming to Steam soon). There's only about 3 pieces of Chiptune on my SoundCloud, but there are several others that have come out of Mutant Chicken's soundtrack.
If you are interested in working with me, you can contact me via twitter: @ccolongames, or via email: firstname.lastname@example.org. Please contact me soon as we only have a couple days left till GBJAM is over!
Hope to hear from you!