Welcome !
If you have a Windows XP or Vista machine, you can make that disk yourself.
Just download the OS from
http://users.skynet.be/emxp/Additional_downloads.htmand copy it to a disk with OmniFlop (which natively supports EIII in its latest version - otherwise use the Emax disk format of OmniFlop).
Make sure that you use an *internal* floppy drive, not an USB one. If you haven't one, ask a friend to use his or her computer
In theory you also have to use DD disks (720K dos) but my EIII OS disk is a newer HD disk (1.44MB dos) with a piece of tape on the HD hole which acts like a DD one.
Success.
///E-Synthesist