Unfortunately, it isn't clear at all where to best obtain the sources.
Since Google Code is going read-only soon, it would be nice to have a canonical location outside of there.
In 2010, there was a post on the mailing list:
https://groups.google.com/forum/#!topic/strongtalk-general/S...
But that GitHub repo has been idle since 2010:
https://github.com/talksmall/Strongtalk
It seems other people have also tried exporting from Google Code to GitHub as well:
https://github.com/szKarlen/strongtalk https://github.com/rvedam/strongtalk https://github.com/rmacnak/strongtalk https://github.com/Michaelangel007/strongtalk https://github.com/DmitryVSkiba/strongtalk https://github.com/emanuelpeg/strongtalk https://github.com/liutanyu/strongtalk
At that point, I got distracted and moved on to something else of interest at the time.