you could probably make it pretty easily.
just get some dark liquid, such as reduced coffee (boil coffee until its reduced to 1/3 its original amount) then splat it on some heavy white paper, in the proper shape, wait for it to dry... scan it, and in photoshop or gimp or something simply do some curves to increase the contrast so that the paper is solid white, eliminate the paper, then... figure out the proper extension to save it as, and there ya go.