I presume you tightened one of the acorn nuts on the valve cover bolt too much causing the top of the bolt to snap (ask me how I know

). In any event, you will need to order another bolt as the size and thread pitch is different on each end. Information for the bolt is as follows:
Side that connects to the block: 8mm (diameter) x 1.25 (thread pitch)
Side that secures the valve cover to the block with an acorn nut: 6mm (diameter) x 1.0 (thread pitch)
There are five bolts with a part number of 90011-PNA-003 and one bolt with a part number of 90012-PNA-003 that secure the valve cover to the block.
How about some rep for such a fast answer to your question?