Where can I get a new key board for ASUS S300C notebook?

Hi!

To get the new keyboard you need you should first look on the popular shopping sites such as eBay or Amazon. If you can not find what you are looking for, you should take a look at aliexpress.com . They sell a lot of spare parts for many devices. Just search.

Also, if you are unsure of your own repair skill or if fear you will break the laptop even more I recommend taking it to a local computer store or look online for someone who might fix it for you (for a fee, most likely, but it shouldn't be that expensive nor should it take long if you provide them with the part).