You need to get the Macintosh/Utilities/Network_Access_Disk_7.5.sea.bin disk image (from the Apple site). This'll create you a startup disk which you can start you machine up with. I can't remember what does/doesn't come on those disks in terms of disk tools so give that a try first and see.

To actually create the floppy disk you'll need to use one of your other Macs (the 4400 will probably be best). If you don't have Disk Copy already, download Macintosh/Utilities/Disk_Copy/Disk_Copy_4.2.sea.bin (again, from the Apple site), run that (on the 4400) and then use it with the Network Access Disk image (run the downloaded disk image by double-clicking on it, then drag the resultant file onto Disk Copy icon) to create the startup floppy for your Quadra.