其它國家GDP數據應該點搵？

Unfortunately, there is no centralized place for all the information that you requested. However, you can find the GDP of almost any countries by the CIA website (it is from CIA but anyone can browse):
https://www.cia.gov/library/publications/the-world-factbook

For garment exporting countries, a very complete list is on:
http://www.tradeforum.org/news/fullstory.php/aid/300.html

For garment industry in China:
http://www.pr-inside.com/china-textile-garment-industry-report-r789841.htm

For Indonesia:
http://www.researchandmarkets.com/reports/349610/prospects_for_the_textile_and_clothing.htm

For Vietnam:
http://www.researchandmarkets.com/reports/516067/prospects_for_the_textile_and_garment_industry

More on:
http://www.researchandmarkets.com/

I think you should limit your project to a few key countries such as China, Vietnam and Indonesia. These are some of the major players.