GNU Smalltalk is being developed at GNU Savannah, where you can view the project page. For code management, GNU Arch is used which has it's repository at http://arch.sv.gnu.org/archives/smalltalk/. If you wish you can also just go there and browse the repository there.
Getting the latest code
To download the latest code tree to your computer, first install the GNU Arch client (tla). Then issue the following commands:
tla my-id 'My user name <your email address>' # if first-time tla user tla register-archive email@example.com http://arch.sv.gnu.org/archives/smalltalk tla get -A firstname.lastname@example.org smalltalk--devo--2.2
This will create a directory called something like: smalltalk--devo--2.2--patch-28. The last part can be different though.
Actually contributing code
To start contributing code, first join the mailing list. Once you are feeling at home there, you can send patches to the latest archive to the list and they will be included by one of the GNU Smalltalk developers. To create a patch file for on the mailinglist, you are probably best of creating a whole tree changeset (see the tla commands changeset and mkpatch).
Back to GST by example