What sort of thing are you looking for? There are soe companies who specialise in tunning cars in particular Clio ie BB, GDi, Hill power, Ktec but I dont know of anyone who specialises in exterier looks of the Clios.
Im not particulary into exterier modification to cars but I wouldnt imagine many people would be that bothered about having external looks wise specialists. Regards tunning though I would go to a Renault specilaist (one of them listed above) as tunning one engine although very similar to any other car engine can have perculiarities which a specilaist would know about.