apparently that person no longer sells those.Im currently watching this item but on ebay uk, it says there are more than 10 available.
http://www.ebay.com/sch/sunshinewithu/m.html?_ipg=50&_sop=12&_rdc=1
Ran a bicycle shop in the early 80's and there was a device available that mounted to the centerpull brake bolt and barely scraped along the tire. Theory was, as has been mentioned, that it would knock many pokey items off the tire right after it was picked up and before the next several rotations could drive it deeply into the rubber.
Some folks swore by them. I tried them and did not any difference in frequency of flats.
I worked in a bike shop in the early 80s and we sold a bunch of these. I think they were called Tire Savers. I still have them on my early 80s Schwinn Super LeTour which I ride regularly. I have never had a flat due to something penetrating the tire/tube.