ive used vicks nasal spray..nice small dome on the end
there is also half domes in craft shops and tesco had some in their craft section, just stick them on to the end of the correct size dowel rod
the tesco pack had hundreds of differnt size domes, superb
doesnt go much bigger than 20/25mm though
there is also the £1 chewy toothbrush you get in restaurant toilets ( frankie and benny's comes to mind ) they are 30/40