how can i get a replacement key for renault clio 98rt?

Hi i have a blip key but after changing the batteries it still wont work. I was wondering if I need to buy a blade and key etc from ebay or something and then take it to timpsons to be copied to my key?? Would that work?? Or is it more likely that my whole central locking system doesnt work as when I put my key in my drivers door it doesnt open all the doors just the driver door, however the central locking button by my gearstick will lock and unlock all the doors???
Ive tried holding down the lock button in my car and then when immobiliser light stays on and double lock pressing my remote but that didnt work either.....
Id appreciate any help anyone can offer thank you chantelle xxxx