Any decent music shop with a good percussion section should be able to help you.
Alternatively, online is of course an option. (US links below as they are the easiest but you can still search for the same product more local to you)
The djembe you listed has a 14" head (they come in different sizes). If you must get a goatskin head like the original then this is the type you are after, or the same from Amazon
If you just need a suitable head there are other brands that might be a bit cheaper, such as this one