請教:申請加拿大移民, 如何辦理中國無犯罪記錄?

According to application form for immigration to Canada, applicant must provide中國無犯罪記錄 which is issued within three months. I left China for many years and have no connection at all in China. Does anyone know how could I get中國無犯罪記錄? Do I have to go back to China? What about if I could not go back? Thanks a lot.