Is there a source that lists all SCOTUS decisions for, say, the past 25 years, which names justices in the majority, versus dissenting justices (even better, separated by written opinion so that separate opinions "on the same side" can be found)? Something quicker than me reading every decision.
SCOTUS blog regularly does posts on that kind of topic (see, e.g., their Stat Pack) and if you looked at their sources or the authors of those posts, you could probably easily find more. There are people who do that and make their findings publicly available, but I don't know them off hand.
The Supreme Court database (release 2019-01 onward) maintained by Washington University in St. Louis not only allows one to download a vast amount of coded data about SCOTUS decisions, it also allows one to do exactly the sort of analysis that is described in the question and to do it using online tools.
The version of the database that was available at the time the question was posted did not have the easy user-interface that is now available.
Yes, CourtListener has several such graphs charting liberal vs conservative Supreme Court decisions