I've downloaded AppleWorks 5.0.4 and Stuffit Deluxe, but they're both in .sit files. The Garden needs to have the final 68K version of the Self Extracting Archive installer for Stuffit Expander.

It's a chicken and egg problem. You need Stuffit Expander to expand .sit files, but when Stuffit Expander is itself packed into a .sit file...

I found an old Stuffit Expander 4.something, just the main program file. It won't expand any .sit file I've tried.

IIRC, Stuffit 5.x will automatically replace lost resource forks on sit files, not that they need a resource fork.