If it is the diverter, then replacement hose/nozzle/diverter units can
be found at any plumbing supply house/hardware/big box store. The
fitting for the hose is often a PITA to get at. You will need a basin
wrench -- sucker with the handle and funny wrench on the end that
pivots. One is a lifetime supply, but is what you need for working in
close quarters under the sink.