Chris & Dani left a comment on my last post that you can also purchase Silhouette Interfacing at Custom Crops. Thanks so much! I searched before for someone else who sold it but all the people I found had it out of stock so I'm excited to have another source for supplies.
I headed on over to check the site out. It's actually cheaper to purchase the interfacing from them. It would have cost me $19.58 for both types of interfacing and shipping instead of $23.51! You can search for Silhouette Products or here are the links: Silhouette Sewable Fabric Interfacing & Silhouette Clean Cut Fabric Interfacing.
Also, if you are looking for a Silhouette Machine - they have them at Custom Crops for $159 on sale right now. That's $50 less than on Amazon right now! Of course, the extra vinyl and accessories do not come with, but it comes with the basics you need to get going.