Polyfuses are not difficult to find. Several manufacturers, even Littlefuse. I get mine from Jameco (P/N 199938) for 55 cents each (quan. 10).
Mouser and Digikey have them in surface mount, too. Not only good for reverse polarity protection (with diode), but for the occasional short circuit, too. 73, Don,ND6T
Don, ND6T