You know... Like an aged or cracking iron-on transfer. I use Photoshop and Illustrator. You don't always draw it do you?
You can also go to istockphoto.com Even though it's a pay site if you sign up, which is free you can download a free photo and vector each week. And you could use a piece of that to implement into your design.
if you want an easy way that looks pretty cool, try searching for distressed brushes on google =D sometimes it looks better when you draw it out though x]