Not always you may have an official Cisco Service Contract for the hardware, especially the one which is quite old, but you need an IOS or an image file badly to test a feature or two.
You can search for IOS image repositories on the Web. To do so type in the search field the following phrase:
index of ios parent directory bin
intitle:index.of ios parent directory bin
Find the image you need to download.
Then go to Cisco Downloads Centre, search for the image file you’ve just found and compare MD5 and SHA512 checksums. The hash values must be identical. If they are not, this image must not be installed.
Link to a big repository: IOS FTP while it’s still alive…By privilege15