All US companies and foreign firms operating in the US have to file regular reports to the Securities and Exchange Commission:

https://www.sec.gov/edgar/searchedgar/companysearch.html

UNCTAD does important research on MNCs:

https://unctad.org/

Various consultancy firms produce information on global industries and firms:

McKinsey: http://www.mckinsey.com/

KPMG: http://www.kpmg.com

Deloitte: http://www2.deloitte.com/uk/en.html

Boston Consulting Group: https://www.bcg.com/

For information on MNCS operating in Asia, see:

Asia TNC Monitoring Network: http://atnc.asia/

and Africa : http://www.lrs.org.za/mnc/