A team has finished a game with 18-8 singles and extra-base hits 6 times since 1897, most recently Cincinnati Reds on 3 August 1989. That is about one every 73,834 team-games.
Box score for the most recent one ↗
18-2 18-3 18-4 18-5 18-6 18-7 18-8 18-9 18-10 19-0 19-1 19-2 19-3
The whole distribution — Singles and Extra-Base Hits · All 18 shapes