bolt that holds crank pulley on needed

My buddy is adjusting the valves on my 70 dart with the /225. He went to turn the crank and the bolt is missing. I drove it home about 150 miles when I first bought it and have been driving for about a month and the pulley hasn't flown off!. Can anybody send me one quickly (payment would be made just as pronto); or tell me where they are available other than the salvage yard; foot and a half of snow yesterday. Thanks