Asbab al-Nuzul

Salamun alaykum

The occasion of revelation is recorded only for some verses of the Quran not for all of them. You can find them in any book of tafsir like Majma' al-Bayan or Al-Mizan. It should be noted that not all those reports are reliable and sometimes they contradict each other or even contradict the Quran. Hence, one should be careful about the source from which these reports are taken.