There is an exemption to the DMCA for vintage software, more specifically, software sold on floppy disk.  Older software sold on a CD-ROM is a gray area, and it greatly depends on the software.  So a rule of thumb is to stick to software that was only sold on floppy disk, and you should be safe.  But I'm not a lawyer.

The problem with Macintosh Garden is that I've stumbled upon more recent software that couldn't possibly fall under abandonware.  So it's a mixed bag.  You'll want to be careful.