Biden/Harris: https://www.whitehouse.gov/briefing-room/statements-releases/2023/04/18/the-president-and-vice-president-release-their-2022-tax-returns/
Romney: https://www.washingtonpost.com/politics/decision2012/romney-earned-nearly-14-million-in-2011-paid-141-percent-tax-rate-campaign-says/2012/09/21/e62e5096-0417-11e2-91e7-2962c74e7738_story.html

Biden and Romney have released their tax returns.