I also study annual reports but have not found a reliable database. I tested several for my doctoral thesis but found ALL had flaws, without exception. Typically arithmetic errors, different aggregations to what I sought or where amounts were not classified consistently from year to year.
In the absence of reliable data I now do it the hard way: obtaining the annual reports I need and extracting the data myself. At least those reports are readily available online and you then have full control of data quality and can trace it back to source.