I've never found supplies at either yard sales or thrift stores. I mostly stick to Michaels and Joann's. There is a scrapbooking store near my house but a lot of the stuff is expensive. I only go there when I need something specific that I know I can't find at the chain stores.
My annual binge is usually at the Scrapbook Expo when they come to Orlando. Luckily for DH I wasn't able to make it out there a couple of weeks ago when they were here.