svn co http://codespeak.net/svn/pypy/dist pypy-dist
Warning, this checkout is relatively big. Another way if you only want to look at the sources is via https://codespeak.net/viewvc/pypy/dist/pypy/lang/smalltalk/.
The Smalltalk code is in the pypy/lang/smalltalk subdirectory; you can run its tests (72 so far) as follows:
Happy poking around :-)