Need Startup Disk for OS X

Where can I get a replacement Startup Disk for OS X? I have an ancient iMac running OS X version 10.6.8. When I try to verify disk using the disk utility i get a message that my disk is corrupt and needs to be repaired by booting from the startup disks. Unfortunately the OS was already installed on my computer and I do not have any startup disks. Can I find them anywhere? I appreciate your time and suggestions.