"I can't find direct trains with earlier dates"
You can't find the direct ECs leaving Munich at 7:17 and 12:33? I can. Are you using the Bahn website? Hint: If you type "Zurich" for the destination, the Bahn will give you Zürich Airport, because Zurich is the spelling international travelers use for Zürich Airport. If you want the town, use "Zürich" or "Zuerich". To specify the main station in town, use Zuerich HB.
Today, the Bahn won't show fares (Savings Fare or Std Fare) past July 12, because they only show fares if they offer to sell ticket online, and they don't sell those tickets more than 92 days in advance.