Touringplans.com has a reservation finder. It's free, and it will contact you when it finds the reservation you're looking for. I've had luck with it a couple of times.
You do have to create an account to use it, but it's free to do so. You should be able to find it on their website in the Dining section.
I think I've seen another free website that does the same thing discussed here recently, but I can't remember the name right now. Hopefully, someone else will know it for you.