Where can I easily find best-paper-award-paper of a conference?
Unfortunately, there is a lot of variety in how much effort different conferences invest into making the information on best papers visible and long-term available.

If you're lucky, the website of the conference lists previous best paper winners on their website. Sometimes this only applies to individual editions (years) of the conference.

In a majority of cases, this might not apply. In these cases, you might be able to retrieve individual award winners by googling for search strings like  (if the conference name is ICSE), &quot;ICSE Best Paper&quot; and &quot;ICSE Distinguished Paper&quot;. Such search strings may lead to tweets and researcher websites of award winners.

Another option is to contact the steering committee of the conference and ask for the list of best papers. This might have the positive effect of raising awareness that there is interest in this information, which might at some point lead to more efforts into making the information available online.