Didn’t think the NT at Langdale took bookings? They didn’t used to – was a first come first served kind of arrangement!
Brotherswater is a good option – they have a (good) pub more or less on site. Limefit Park at Troutbeck is walking distance to The Mortal Man and The Queens Head (which is ace)… erm… there is a good one in Cartmel if you start struggling too – with some ace pubs in the village (the campsite is actually in the village, so it aint far – the riding is suprisingly good too!)
No chance of getting into the Old Hall in Consiton I wouldn’t think – but worth a try just incase. Wasdale *may* be worth a try too cos it is sooo bloody far away from the M6 that a lot of people never make it there 😉 Try the NT site and the Wasdale Head (though that had bugger all facilities last time I used it… which is probably 10 years ago!)
Can’t think of any more off the top of my head… there was one down in Borrowdale that I forget the name of, and was usually quiet due to no facilities there either (well – basic washing facilities in a shed, but that was about it – ace site though!)