System 7.5.3 is a free download from Apple:
http://www.info.apple.com/support/oldersoftwarelist.html#system
As that is all of 19 disks and thus an overkill, however, and assuming that you need merely to boot the machine in order to "bless" that folder, I'd recommend that you download the "System Enabler 040" from the same site and pop it into your 7.1 Disk Utility floppy disk's system folder. The Q800 should boot from that altered floppy.
http://www.info.apple.com/support/oldersoftwarelist.html#system
As that is all of 19 disks and thus an overkill, however, and assuming that you need merely to boot the machine in order to "bless" that folder, I'd recommend that you download the "System Enabler 040" from the same site and pop it into your 7.1 Disk Utility floppy disk's system folder. The Q800 should boot from that altered floppy.