Good day,
If you want the offical Renault product...
The part number for the original cup splitter is:
8200248910
Price is roughly:
Retail - £128.51 + VAT
Just call Renault spares (they had that on the system as a 'front spoiler') and quote that part number.
The other popular choice as Gman said is the one that
www.k-tecracing.com offer (a carbon fiber one) which is cheaper but doesn't fit right to the edges of the bumper by a marginal distance.
Others use the Megane splitter, some rubber tube, a Seat Cupra splitter or one from a PUG 307.