I can't tell from the picture if you need double hook or a single. I found double hooks on EBAY. Search 'bed rail hooks'.

or Van Dyke's

Yep....sure have seen those brackets.
perhaps this site would have something?

http://www.antique-hardware.com/Bed_hardware
Or you may have to see if you can find a junker old bed and swap out the rails....or maybe just the hooks.

linda, thanks for the site!

Thanks for your help, everyone! The strange thing about the bed rail bracket is that it has a metal piece across the middle that sits tightly against the wooden cavity -- there's no room for a hook to latch. With a renewed sense of purpose, I found this website (http://robinsonsantiques.com/bed-hooks/bed-hooks.htm) that seems to have a big collection of weird bed rail fasteners. I'm going to send them an email to see if they can help.

I'm looking for rails that match those pins. Any ideas where to start?