You may be thinking of 1973, when Aaron, Davey Johnson, and Darrell Evans all had 40 or more HRs (in fact, Aaron's 40 was only 3rd on the team. It was definitely a career year for Johnson (his next highest season total was 18), but Evans had many other high totals (including another 40-HR year) and had 414 for his career, so nothing that year was out of the ordinary for him. Except that he hit 40 home runs at age 39 and in only 120 games. I know it's not technically the most home runs he hit in a season, but it's pretty ridiculous.