The project is up on code.google.com
This makes it available for SVN download (Anyone who can set up a compiler can build up-to-the-minute versions of the program).
That wont help folks that arent comfortable with SVN or compiling programs, but:
(1) There is a web interface to the repository
Go to
http://code.google.com/p/stonesense/source/browse/ and you have a view of what you would get if you did an SVN checkout.
From there, go into the trunk area via the links on the left, and you will get a list of files including the object.png file.
You can also get at the configuration files from the trunk/buildings area.
Note that changes made on developers machines wont show up until we upload them, so, for example, I have set up your cages here, but I havent got them as far as googlecode quite yet (especially this close to release, I need to be careful not to conflict with anything Jonask is doing)
(2) We are making the software configurable, so you wont need to recompile it to add more sprites. With the exception of changes to the configuration format, downloading additional sprite data via the web interface will be enough to get new objects (once we get this release with the configuration stuff done)