Go to your local builders merchants where you should be able to order the correct size through Companies such as Bolton & Paul or John Carr Lucy. It may be that your existing door started life as a larger size but was cut down because of the frame size you have so you may not find a door which, off the shlef, will fit exactly. In this case a carpenter may well be required to tell you if the nearest door you can find could be cut down to suit.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!