I don't have any suggestions for you but you can search the State's licensing website for daycares and read about how their inspections went.
I don't know how you would secure "back up" care though...maybe place a deposit somewhere for a certain date and risk losing the deposit if you decide not to switch?
My back-up care is my in-laws, but only for a few months out of the year...When she's sick, I have no back-up care, hence the reason behind me being stuck at home today with a sick baby....
Are there any neighbors around you that you'd feel comfortable asking? Or any churches? Some home daycare people post on craigslist. Never in my area, of course, but depending on where you are, you might find someone.
We had DD in a home daycare to start and the lady called off so many times in the first (and only) month she was there. We switched to a center to avoid this.