Where to obtain a common/weak password list (black list)?
Well, you could just google it!  This is the top 100,000 broken passwords from the UK's National Cyber Security Centre (GCHQ).  It's probably trustworthy. Top password is 123456. Probably shouldn't use it then. That article is dated 21 April 2019, which is a while ago. Not sure when updates will happen, but again, more googling...
Your note could also refer to an internal list of compromises only known to a particular organisation. Companies try not to publicise such breaches if possible/legal, but clearly they happen so lists could be compiled.