It's an impressive piece of work as for a Scheme implementation (saying this as a Scheme implementer myself[1]). I'd love to introduce some ML and static typing in my Scheme too.
I spent some time looking for the source code, then found it at the site one directory up: http://nightmare.com/rushing/irken/irken/ , just in case anyone's interested. It looks like the author does not use version control and Github at all.