For some years, I have extracted statistics on the classroom performance of our students (that is, of EECS and declared CS majors in Letters and Sciences) from the registrar's database. The the complete report contains the numbers. Specifically, the figures given are in units of student-courses, that is, numbers of registered students receiving particular grades summed across some set of courses. A given student, therefore, will be counted numerous times, but the numbers reflect the total load on the system -- on faculty, TAs, etc.
You might also want to look at some plots of particular tables. These plots show how A's, B's, etc. are distributed for each of four cohorts: EECS students admitted from high school ("native" students), EECS junior transfers, and likewise for Letters and Sciences students. There are graphs showing distributions for all UC grades, for lower-division and upper-division EE courses, and for lower-division and upper-division CS courses. For each of the four cohorts, the graphs show the percentages of all letter grades (that is, as percentages of the total number of letter grades given to that cohort). Again, we count student-courses; these graphs do not directly show numbers of students with various GPAs.