The well-known shoes producing province is Fujian, you can search some info. on the internet.
As for the visa to China, you can find a shoe wholesellers in China, and then ask them to provide you a invitation letter for your visa application.
Besides the invitation letter, you also have to provide the requirements below:
1. Your passport with blank pages and at least 6 months validity left before expiration.
2. A truly and completely filled application form affixed with one passport-sized photo.
3. Qualified original introduction letter with the full name, title, date & signature of the issuing person from your company. The letter should state clearly your name, present occupation and position in the company, purpose of the visit, intended duration of stay, city intended to visit, name and address of applicant's business partner in China, items and quantity of goods planned to order and purchase;
4. Any proof of business connection with the inviting company in China (e.g. fax of business negotiation, contract, agreement, quotations of goods, invoices, bill of lading, etc.)