You are probably missing more than just the bolts. This might be what you need:
http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2650Q36L326A1B7IKT&year=1979&make=MB&model=300-SD-001&category=H&part=Exhaust+Mounting+Kit