Hi Neil, I had a look around. It seems that MySaga are no longer with us, though probably in name only. The majority of phones from China and thereabouts turn out to be differently branded devices with the same generic components. There's only one (fairly) reputable company that supplies these parts, I've sent you the link to the relevant shop and items (I can't post the link here for several reasons). There are two parts, which is the norm for touch screens. If the display looks ok (no graphical glitches or bleeding colours, etc) then you may get away with getting the touchscreen only. If the crack has gone right through and is affecting the display then you'll need both. If I were you, and if you haven't already, I'd see how they are attached at the moment. It may be hard to separate them without damaging them both. You may need to apply some heat via a hairdryer to soften any adhesive, then slowly pry them apart with a plastic tool. If you can separate them without any further damage then you should be ok.
Good luck anyway.