I just did this the other day. I went to Advance Auto and bought the strikers there. They were 8 bucks a piece. I then went home and tapped out the hole and wha-lah I've got a bed extender now! You can also find the strikers on Amazon and Ebay. Those are self tapping but I didn't want to wait. Anyway good luck!
Thanks Eric. I will give AA a shot. My ST had an extender at one time and the holes are already tapped. There were two extenders in my area and one for $50 so I said what the heck. Thanks again.