I'm not an expert by any means but I think it is call 'Lienzo quesero' or 'Lienzo para la fabricacion de queso'
Now an address on calle Aguero al 400 (left hand, 30 meters before Valentin Gomez), there is a business for the dairy industry, which sells retail, and has everything you need (cloths, curds diverse, stabilizers, etc.) does not publish on the Internet and are only suppling to small producers, please check that they still in business and report back.