Its called a volute , Richard burbridge sell them (spelling on both names may be incorrect) Homebase deal with RB so will be able to get one for you as will most timberyards that deal with RB . One thing to remember is you will need longer spindles for the volute and a volute newel post . The newel post can make the whole hand rail unstable if its not fixed real good ! And i mean real good ! I recommend taking the newel post down to the sub base if possible and bricking it in .
P.S you will also need the part that takes the handrail to the volute , a small curved piece .
Im sure the pic you posted is from the RB site .
