I actually bought mine last year in Boro at a shop just down from the Rila hotel and they are fantastic. I know you are now going to ask how much but I honestly cant remember as I was in so much pain that I just had to have them. They will not have been more than around £20 quid though. I will go and find the make for you now. How are you for impact shorts because I have great ones of those too if you need advice?
They are made by Spartan Sport who I can't find on the net now, but this is the closest image I can find to what I have although mine are black. I can't really feel them on until my knee hits the ground and then I'm so glad I do.
Hey, i use foam trouser inserts as knee pads. - builders/plumbers often use them. Then long white tubey grips to hold them in place. I find they're more comfy than some other types because they dont dig in behind your knees. Approx £5 from b&q.