Originally Posted by
dsbrantjr
Better get a couple extra when you find them; the intact bolt in the second photo looks like it has cracked. There is also "Sugino" stamped on the bolt head which might be an additional clue to finding a replacement.
The bolt marked "Sugino" is a standard seatpost clamp bolt and almost any LBS will have them. And, yes, the missing bolt is indeed a "Chicago Screw". The OP may be able to find a suitable one at a well equipped hardware store or a Fastenal shop.