67 Barracuda bench seat with fold down armrest

One of the original bolts for the fold-down armrest in my 67 Barracuda is lost. These are the round headed bolts that are tightened with an Allen wrench. I substituted a bumper bolt for the lost original. Works OK except that it comes loose over time because I can't really tighten it. Is there a source for new replacement bolts, or is this strictly a junkyard item?