Hi Kaisung_24. Welcome to Geekhack. I have been in hibernation a while now myself.
Have you got a hardware store around? I would just take the screws you need more of to a local hardware store and see if they have a tool for determining what sort of threading you need. It is usually a plate with various threaded holes that labels them all. If the screws thread in, then that's what you need. You may not find the exact same length of screw, or head type. Just get as close as you can.
If you want, once you know the specifications you need, you might be able to find something closer online.