http://www.flickr.com/photos/9574684@N07/696297346/

It was also used in the Mosaic ad and there is a high res download of that available at:
http://ronpaulmosaic.com/download.htm

Hope this helps,
eb

In fact, looking closely at that photo, it's a scan of a picture, not a digital photo.

Beat me to it. Other than that, the House public affairs office may have a higher-resolution file.

http://www.house.gov/paul/images/ron_paul.jpg