China's decision to tighten COVID restrictions in the country could reduce iPhone production in a supplier's main factory by as much as 30% possibly making it hard to find certain models in stock. A source knowledgeable about the situation at Foxconn's main facility in Zhengzhou told Reuters that the drop-off in production could take place next month. The contract manufacturer is looking to make up some of the lost production at its factory in Shenzhen city. Foxconn employees in Zhengzhou are leaving the facility On Sunday, Foxconn said that it was working with some of its other manufacturing facilities to…