+1 shutterstock or adove stock archives.
not a fan of catalog artwork for this stuff, unless its already part of the whole graphic i intend to use like auroragraphics does for their swoosh/flags/stripes package.
if you're customizing a logo or a shape, then i've found it easier to just watch youtubes of similiar things, such as "torn paper" and then apply brushed/gradient effects to the metal layers to make it metallic. Feels like more work, until you get the hang of your pattern/steps to build it from scratch to fit it the way you like ...rather than trying to warp/manipulate cut&paste yourself into a corner.
tutorials available for both
illustrator and
photoshop.