oven/cooker replacement control knob for hob

Hi
Can anyone tell me where I might find a replacement control knob for the hob on my gas oven. There are four burners and one of the control knobs has broken in half – so that there is only a thin ‘D’ shaped metal rod sticking out … and also, are these universal fittings? because I don’t know the make of the cooker … its white with a glass pull down lid !!!

thanks in anticipation
V