No recipe inventory, you should write your own.
It wasn't clear from your post if you are looking for actual reciepes or a software managing them.
If the former, than I see why your search queries yield no results. "Open source" usually associated with software, open written works usally ha ve some kind creative commons license. Search for that instead
Do not ask for the time zone, ask for the city. Than use a tool for the task. People are stupid, and they don't necessarily know the name of their time zone, even during DST.
I used website this before, you just type the city names and it will show you which time is good for which participant: https://www.timeanddate.com/worldclock/meeting.html But I'm pretty sure a lot other websites exist to solve this.
The problem in your story was not time zones, but you didn't use the correct tool for the task.