Hi everyone,
I have had some experience with constructing things, and I am pleased to say that the tripod hole for cameras is a standard M6 thread. That means you can buy a M6-sized bolt from any DIY shop and it'll fit.
The problem is different screws and bolts all have different thread specifications. You need an M6 sized one. They're so cheap you probably can't buy just one. I buy them in 100g quantities! One probably costs like 2cents.
Try provision shops or 'wu3 jin1 dian4's and ask for a M6 hex bolt, about 1.5 inches long is great.
p.s. I'd like to add that you should only get galvanized steel ones (the cheapest most common ones). Stainless steel and brass bolts usually have different threads. Best if you bring your camera (or any pns camera since they all fit the same tripods) to test!