Don't know about patches, but Roger Johnson's Welcome to America site has a lot of HP logo merchandise available. I have the poster that I got through the Merc and am looking at it right now. Very cool designs on each of the HPs. If you really want patches, you might be able to make them out of baby bibs. Not sure if I'm serious, but it would work.
http://www.cafepress.com/wtoamerica/5927157