Another option is to play progressives. I haven't played an open league or a theme in almost ten years. But, if you want to keep doing so, progressives will acquaint you with different players from different eras.
Also, try to pick parks that have a favorable pitcher rating. Among my leagues, I've used South End Grounds, Braves Field (Boston), Shea, and Yankee Stadium. Also had some success in Dodger Stadium.