I've just done the same thing, and havn't got a spare either !
It's not so bad for me, cause i'm not allowed to drive till march anyway, but still a nightmare.
Renault just told me that the fob is "on the shelf" and that they can program it to suit the car's alarm/rcl/imb.
They said that the fob's £80 then another £80 to program it. It has to be a new fob, they can't reprogram keys that have been used on other cars.
They gave me a code (gave him the reg) to get the key blade made, £7 from the auto locksmiths. (surely they shouldn't do this over the phone, I could have been anyone ?)
I think i might try one of those "new" fobs off ebay, its only a £10, you never know it might work...having said that those friendly people at Renault 'll prob'ly charge me £80 to tell me that it doesn't work !!