You can download this from the github project.
I compiled Gambit Scheme for the iPhone and have been working on a game using it ever since. The above github project should help you get started doing the same. Specific instructions are described in my blog post about it.
You should debug it with the debugger described in this post. Please contact me if you have any questions trying to work with Gambit Scheme on the iPhone. The developer environment is unfriendly and you'll most likely have problems getting the debugger working.