Testing Roberts's Law: data request on CEO pay and company characteristics
There are plenty of papers studying CEO pay and firm size empirically. Check a long list here. Some examples of data sources:


US: Execucomp, used by Gabaix, Landier, and Sauvagnat (2014).
UK: Hemscott  and Datastream, as used by Ozkan (2009) or Gregg, Jewell, and Tonks (2011). Also, BoardEx and Datastream, as used by Tarkovska (2017). You also have the Bureau van Dijk FAME dataset (used by the Bank of England, e.g. here), but it is proprietary.
Germany: handpicked from financial reports as in Heimes and Seemann (2012), or data obtained from the consulting firm
Kienbaum, as in Fabri and Marin (2015).