If it's just an ordinary bolt, try Ace hardware. They have all sorts of metric bolts. Most auto parts stores also carry them. If the bolt is a big one, then try a Caterpillar dealer.
Look for the number of slash marks on the head of the bolt. You'll want at least a grade 5. Be careful of cheap, Chinese bolts. They've been known to be graded a lot higher then they really are. You can be assured of getting high quality bolts from Caterpillar. Try the same places for the washer if it's an ordinary flat washer.
