That’s so weird. I just had to do this today for an old copy of CS3 for my company. I grabbed the trial from ProDesignTools, input the serial number we had on hand, and we were off to the races. I know you say you tried that and it no longer works, but did you follow their instructions exactly? You have to first log into the Adobe site with your Adobe ID, then start to download CS6, cancel that, then bounce back to ProDesignTools and then the links will work. Without logging in to Adobe first, the links all give a “file not found” error. I just gave it a quick test and the CS4 Production Premium started downloading.
Good luck!
https://prodesigntools.com/download-adobe-cs4-and-cs3-free-trials-here.html