You can make one, as previously mentioned, or you can purchase one. This site has a few of them in the site store and amazon has some pretty good ones too.
I have added a list to this section of the site called "Wood and Wands" if you are going to use your wand for a particular purpose it might help you find the wood most associated with said purpose.
Also, keep in mind that you don't necessarily need to use a wand. You can just use your hand and fingers to direct energy. As with most magical tools, you don't need a wand unless you think it will help your focus in spells and rituals.