If you’re asking for the actual firmware ZIP file you’ll need to ask a favor of your Cisco account team; fully deprecated models are removed from the software download center - and anyone else sharing it directly would be violating their licensing agreement. You can search the internet, of course, but a downgrade may not even be possible. Hardware revisions (ie different chips on the PCB) often have minimum firmware levels. That documentation is no longer available though. And, IIRC, firmware signing was introduced sometime around the 8.x-9.x timeline; you can’t downgrade from a signed to unsigned release.
