Thanks for the reply so far guys.
I have spoken with london gliding club just now, which is near where I live but they said they just use standard car seat cushions and dont have any spare.
BackPacker, i was not aware that we can use cushions of any material (apart from explosive material lol) so I will check that with my instructor. If that is the case then my search is a lot easier as I can probably just use a sofa or car booster seat cushion. Also i dont think the rudder pedal extenders are available for the eurostar according to my instructor. The cushion I have used for the last few lessons has been great and worked a treat.. but as i mentioned the owner has now left the club and taken it with him.
Cats_five, yes dynafoam is the material i was quoted by my instructor. i found a site that actually makes them but they have 1 month turnaround and need precise seat measurements. I really need one by saturday for my next lesson so its quite urgent!
Whirlygig.. that looks good, althought it doesnt support the entire back, and I might need 2 since I need one to sit on as well haha.
However, if i am indeed allowed to use one of any material i may just get that one, since it has worked for you, and as you said.. it may also be good for my posture to help me see out better. thanks very much for the link.
Ideally im after a site or person whom I can just buy one from today, as i need one before sat!
thanks for your help