Here is the year-to-date winners and losers list of the Superinvestor portfolio, as defined by Dataroma.
The Large portfolio includes the stocks held by all of the superinvestors, and the Small portfolio includes only the holdings of Berkshire Hathaway, Markel, Sequoia and SQ Advisors.
This is usually run on Fridays during the day and sometimes on Thursdays (check the date at the top of the tables for date of last update).
Note: As of May 19, the database source change so there may be many missing tickers, (Yahoo Finance API had a comprehensive list but was shut down) and the stock prices may be from the previous day.
Note: The free closing prices API has been shut down, so I can't update this until I find another source...