A team has finished a game with 21-1 singles and extra-base hits 5 times since 1897, most recently Kansas City Royals on 29 July 1995. That is about one every 88,600 team-games.
Box score for the most recent one ↗
20-6 20-7 20-8 20-9 20-10 21-0 21-1 21-2 21-3 21-4 21-5 21-6 21-7
The whole distribution — Singles and Extra-Base Hits · All 18 shapes