Instead of precise percentages, you'll typically find ranges or broad descriptions like this: Stanford generally reports a student body with significant representation from Asian Americans, followed by White students, then Hispanic/Latinx students, with smaller but still notable percentages of Black/African American, and other racial/ethnic groups. International students also comprise a significant portion of the student population.
To find the most current data, you should consult Stanford's official website, specifically their Institutional Research office or admissions statistics pages. These reports usually include breakdowns by race and ethnicity, but keep in mind the limitations mentioned above. They are also likely to provide separate data for undergraduate and graduate students.