My old post for making a floppy disk image didn't work as described when I tried it recently. Here's an update.
The hdiutil command can be used to create the image.
$ hdiutil create -layout NONE -fs MS-DOS -sectors 2880 floppy
Then use hdid to output the name of the device file created.
$ hdid -nomount ./floppy.dmg
Use the output from hdid to create a mount point and mount the image.
$ mkdir /Volumes/mnt
$ mount -t msdos /dev/disk2 /Volumes/mnt
Now you can copy your files to the disk image. Use the usual disk "eject" to unmount if you like.
