Last minute bookings App

I find it quite time consuming to search for a site on Thursday night having made a snap decision to try and get away for a weekend (Friday - Sunday inclusive), especially when the weather forcast is good! What I would like is an App on my phone where you could simply put in a desired location and dates and be presented with a list of available sites and pitches to phone using the App. To be honest if I phone a couple of sites and they're booked up then I tend to give up and the caravan stays on the drive. And I simply won't book in advance cause to be honest my idea of a weekend away does not include 3 days of rain! Has anybody got any tips for snap decision caravaning weekends? Especially on the south coast!