If you are in China (outside US) and lose your green card there, you need to go to the US Consulate to get the transportation letter to enter US, then file I-90 to get the replacement. No choice.
See these websites for applying for transportation letter:
http://www.immihelp.com/greencard/lost-stolen-greencard-transportation-letter.html
http://guangzhou.usembassy-china.org.cn/transportation-letter-application-for-losing-green-card.html
