Waterloo Road series 1 2 and 3 our on DVD?

I am a big fan of Waterloo Road and the 4th series of Waterloo Road has just finished. I really enjoyed the 1st and 2nd series and would love to watch all 4 series again. At the end of an episode it said series 1 2 and 3 were out on DVD but it never said where you could buy them. Anyone no where i can buy them. And also how much they are? I live in Harrogate so anywhere in London or wherever is no good. Please help.