7.5.3 used to be downloadable from apple for free as abandonware, so you may be in luck. The website is gone, but wayback has the URLs. Start with [0] and edit the XXofYY for the rest. Getting a legal copy of the Macintosh ROM is what'll get ya.
If someone mirrors a company's free download page, you can't legally download from the mirror, unless they have redistribution rights, which they don't. A free download from a company means that you are permitted to download from the company, not from anyone else who has a copy, not even a mirror.
Again, probably nobody will arrest you for this, but nobody's likely to arrest you for conventional piracy either.
This is not a mirror. This is apple's actual official download location for this software. Sorry I should've been more clear.
Unfortunately as a result, they're packaged in self mounting Disk Copy images, so you'll need an old mac to unpack them. It's possible someone has developed a tool to extract regular disk images from these files by now.
[0] https://download.info.apple.com/Apple_Support_Area/Apple_Sof...