Many thanks to the World Bank for building and posting a database of the freedom of information laws for many (not all) countries.
The database is part of the World Banks’ Public Accountability Mechanisms to keep government operations honest and transparent.
Freedominfo.org points out:
The Bank does not rate or rank the countries, but the database is expected to be a trove of information for comparative research. The Bank now is moving into research on FOI implementation issues.
The database collects information about FOI laws in seven broad categories with 30 subcategories.
Furthermore, the Bank does not score countries on their openness laws. But at least there is a list to work from.
After going to the Public Accountability page, click on the country you are interested in. Then scroll down to the FOI link.