Khanivore - regarding fliers, I've seen photographers giving out just a strips of A4 paper with their details on it at the finish. You could do this very cheaply, explaining your cause, and in one of two ways - either get a buddy at the finish line to do it, or ideally chum up the RO and get it into the goodie bag if there's one on the go.
With regard to ark run, our run has an official photographer who turns up occasionally. Other weeks folk take pictures and post them of Flickr. Is there any way you could sell your pics from parkrun too? Not sure how many would purchase, but if you're there anyway it's worth a shot.