There are two good websites. They are:
I like Cafepress
You can get them at Walmart or on eBay or Craig’s list
You can find some Twilight shirts at Borders. That’s where I got mine and I’ve had it for a long time and its still in perfect condition. As for backpacks you can either go to Target or K-mart.
I go to Hot Topic, the shirts there are 22 and I wear my mine all the time and it doesn’t show, it looks brand new! They also have TEAM EDWARD stuff, no Jacob.