Numerous Chinese manufacturers, especially in Foshan (the "Ceramic Capital"), produce 600x1200mm black marble-look porcelain tiles, with key suppliers like Foshan Urban Ceramics, Intop Ceramics, Foshan Colorgres, and Shenzhen Sunnda Industry offering options from full-body polished to soft-polished, often mimicking Nero Marquina, available via B2B platforms like Alibaba and Made-in-China.com. 

When sourcing, use terms like "600x1200 black marble porcelain tile," "Nero Marquina porcelain," or "large format black tile" on these B2B sites to find specific manufacturers and request quotes.