Door knob for 1930's door (Rowlands Castle PO9)

I wondered if anyone has a spare door knob for an inside 1930's door please. My son is refurbishing his wreck of a house and the other side of the handle has broken ( the white one) on one of the doors. There are also some other brass ones ( see other photo ). Anything to match please or any other knobs in a pair would be welcome. They are the type who fit onto a bar that goes through the door so the handles can turn. Many thanks much appreciated.