Does a company exist that made its carbon neutrality data open source?

Data and open source is hard to define in context of carbon neutrality. If you are looking for sustainability reports there are plenty of companies that publish that.

For example: Google Cloud [0]

Find out which companies have claimed to be carbon neutral in the first place. Also you can look into investors relations section of these companies. I don't know if you will get a spreadsheet or database but you will get some insights.

0: https://cloud.google.com/sustainability