the 'keep' (I think it's called) to my UPVC front door needs replacing?

I need to buy a new part for my UPVC front door. It's the part that the latch fits into (the 'keep'?)to stop the door from being opened from outside. I've been told by double glazing firms I would need to replace the whole espagnollette strip at acost of abnout £200!!!. Does anyone know where I could get hold of JUST the part I need? (I think the make is 'Roto'.)