I went off Googling and apparently the most runs scored in a 3 game series is 78 runs between Brooklyn and the Pirates in 1950. The series ended 2-1 to Brooklyn.
Now we just played a 3 game series where the Cubs swept the series and 64 runs were scored. So if the “you” in your post means one of the teams and not the Cubs specifically, the most runs scored combined in a series where one of the team is swept could be the series that was just played.