I needed this, and I couldn’t find it within five minutes of searching, so I went to Wikipedia’s list of LGBT pride flags and snagged all the SVGs and turned them into a bunch of Illustrator brushes. All of these files seem to be Creative Commons so this is, too.
Grab this and put it with the rest of your brush files: pride flags.ai – go forth, and draw the queerest fucking things you can think of! I sure needed it for some super-queer art.