Definitely check a health food store (in person or online). I'm not sure specifically where online you could buy them, but I'm sure a Google search will produce results.
I buy my jojoba oil at a local health food store. Olive oil and castor oil you should be able to find at a grocery store. Grapeseed oil is a great base/carrier and you can also get that at a health food store.
Trying to get started with the oil cleansing method, and I was able to find castor oil, jojoba oil, and almond oil right at Whole Foods all in their beauty dept. Now if I only knew where to begin and what to do with what I recently bought!