Hello, according to Chapter 4 of GB/T11-2006 Common V-belts for General Transmission (note: commonly known as V-belts), the V-belt structure consists of rubber canvas, top glue, buffer glue, core rope and bottom glue. The rope you are talking about is a core rope (the nylon rope you see), and polyester rope (such as polyester thread) is usually used.

As for where to supply in large quantities, it is no longer a problem. China is a fully market-oriented economy, with developed spot and futures markets, which are in line with international standards and synchronized prices. You can check online and find a professional and formal trading company to buy the goods you need.