Alex Shinn's Chibi scheme, weighing in at 50kB (but with a dependency on the Boehm garbage collector, which weighs >1 Mb ...), might fit the bill.

Some links

1. Andy Wingo (main Guile implemetor)'s "buyer's guide" to Scheme implementations - http://wingolog.org/archives/2013/01/07/an-opinionated-guide...

2. Chibi Scheme homepage - http://synthcode.com/scheme/chibi/