Not every type of audience demographic is tracked by premium market research tools. Robust data tends to revolve around cohorts of demographics who spend massive amounts of dollars on products. For other types of demographics try locating associations, agencies or government statistics that may try to estimate counts. Statistical Abstract of the United States is a great starting source for government data as are government agencies at the federal and state levels. Free access is available through the library using the link below.
For data about specific college or university populations visit the school websites. Public schools share more data about number of students attending than private schools and most schools will not release specific characteristics fo the student body. For example RIT makes some available here https://www.rit.edu/overview/rit-in-brief and here https://www.rit.edu/fa/irps/dashboard Note that the second source has some data restricted.