how to get specific android OS for testing

I have a problem that only happens on Android 8. I tried the emulators and was not able to recreate the problem. I need to find a way to get a test device with android 8 on it. I tried Amazon a few times but each phone that advertizes having Android 8 would show up with Android 9 or something else. I currently have a Device: Galaxy J7 2018 (J737A). Questions: - Is there a way to revert my device to android 8/8.1? I have looked and have not found anything for this model number. Need the stock version. - Is there any online store that sells devices where users can choose Android OS? - Is there any other way to recreate a bug and debug on specific versions of Android e.g. Android 8 Oreo?