Where can I find specific Apple firmware like early 2011 SMC 1.69f3
For most people, I recommend always going forward, never backward. I’m sure someone has squirreled away copies, but I don’t have any source I trust to get old firmware.
There are ways to flash firmware without Apple’s loader process - How to downgrade SMC firmware

As you notice, since the updates now happen when you install macOS updates and
upgrades the older Apple page is archived and not maintained or migrated to the new hosting support sites.
In the case you seek to down level, I've not ever seen that work. I’m not saying you couldn’t be the first case to achieve that, but the issues tend to be failing hardware and not that the newer firmware has some bug Apple doesn’t then fix with even newer patch.
I’m not saying you’re wrong, just my experience is this hasn’t helped in the past. I hope you prove me wrong in this case and can report success getting the code and that it helps as you expect. Documenting it publicly and the checksum of known good firmware will be a service to everyone.
Keeping “obsolete” or “vintage” gear in full operation makes me very happy and is a worthy goal.