Surely Renault have them. I bought an obscure R5 TX gearbox mounting from tham for £35 plus VAT, so I'd expect they would do the R4 part. Lifestyle Renault in Tumbridge Wells can do mail order if you can't cope with your local dealer (I can't cope with mine).
Bet the French can get them cheaper. I'm planning to do one of these intensive French courses in France so I can find parts more effectively.