I think your choices are...
Get someone to send you a Workbench 2.1 install disk.
or
If your old hard drive still works and has Workbench 2.1 on it you have couple of choices.
1. Hook the new and the old harddrive up at the same time. Run HDToolBox, setup the new drive, and then format it. Then just drag and drop all the Workbench files from the Old hard drive on to the new harddrive.
2. Download the Workbench 2.1 disk from some where or get someone to email it to you. Then format 720K PC disk using the Amiga 600 (Workbench 2.1 should have come with cross dos and presumably it would be on the old harddrive) use that 720K disk on the PC to copy the files you download over to the Amiga and make your own Amiga Formatted install disk on the A600. Might want to LHA all the files or use an ADF image (and an UnADF-ing program once the file is transfered on to the Amiga) when transfering them on the disk, because if you just copy the files on a PC formatted disk all the names of the files will be changed to 8.3 format.
EDIT
You could search the internet to see if it's listed somewhere exactly what files are on the Workbench 2.1 install disk.
Format a floppy disk. Open up a shell and type:
install df0:
(This will make it so the floppy will boot when you reset the machine. )
Copy the files you need from the HD to the floppy, reset, and you should have a booting install disk.
