Most SCOTUS opinions are rigorously sourced. They’re usually also well argued. The recent spate being an exception, in particular anything written by Alito.
They're rigorously sourced in that some set of underpaid clerks is tasked with surfacing their best guess as to what material is most relevant to the court, with optional fact checking competing for their time.
https://www.propublica.org/article/supreme-court-errors-are-...
So the sources exist, but whether they're quality is another question.