Since the textile quotas for China has been lifted, most of the shirts you see today are probably made in some factory in China. Even brand name shirts have been outsourcing their production to China, and these are secrets that are unknown to many.

We'll here's one supplier from China that supplies casual and business shirts.

Company Name: Shanghai Lovage Textile Co., Ltd.
Contact Person: Philip
Address: Room 3002/3, Building C, No.1066 Jin Sha Jiang Road, Shanghai City. China
Zip: 200062
Telephone: 86-21-52824461
Mobile Phone: 86-13601635640
Fax: 86-21-62650745
Website: http://www.lovagetrading.com