The primary source is the IMF's International Financial Statistics (IFS) database. The concepts and definitions are from the Fund's A Guide to Money and Banking Statistics in IFS.
For most countries, the money supply broadly defined comprises money (IFS line 34) and quasi-money (IFS line 35), the normal forms of financial liquidity that economic transactors hold in the monetary system. By definition, holdings of nonresidents and the central government are excluded.
In some countries, other (nonmonetary) financial institutions may also incur quasi-monetary liabilities, that is, they may issue financial instruments on terms similar to those for quasi-money. Where these are significant, money supply broadly defined is a measure of liquid liabilities comprising the monetary and quasi monetary liabilities of both monetary and nonmonetary financial institutions.