Papua New Guinea Passport holder wishes to apply for China Business M visa with letter in Singapore

Dear China Travelguide. Many of my friends and customers from Papua New guinea travel through Singapore and some wish to visit PRC for purpose of buying machineries and goods for direct export to their home country. Please advise if they can personally apply in Singapore and with return tickets to Papua New Guinea can they travel to PRC with return tickets to SIngapore? Thank you very much.

Paul Mah
Singapore