Install OpenCL on Raspberry Pi with Raspbian Stretch OS
Download Raspbian Stretch
I believe you are looking for an older download version of Stretch rather than the smart arse answer :
Older download version of Raspberry Pi OS
64bit version of Raspberry Pi OS
This gives all previous versions released if you don’t want buster at the moment.it doesn’t however give an option including recommended software although that’s easily resolved once booted