Q: Where can I download System 7?

Try here -

http://ftp.iinet.net.au/pub/apple/US/Macintosh/System/Older_System/

You can go back up through the 'parent page' link to get to other things you may need, such as a cpu-specific enabler or updaters.

Is Apple intentionally hiding this ftp site?

Not as far as I know. Apple took down their source-pages for that older stuff without comment or mention of other sources.

I am currently running System 7.5.3 in the emulator BasiliskII (part of the E-Maculation project - Google it). Luckily I had most of my old software and documents of that time squirrelled away.

I also run OS 8.6 in the SheepShaver emulator produced by the same people.

Setting them both up was slightly complicated, but they have excellent instruction manuals for both, including where to get old school ROM (for 7.5.3) and new school ROM (for 8.6). As for the Mac systems themselves - E-Maculation provide a link for 7.5.3, and there are many Mac systems classed as 'abandonware' at http://www.dreamsupport.us/downloads/ar ... /index.htm