If I were you, I would try phoning an emergency vets and say to them its because your own vet isnt taking the problem seriously enough....he is old and older cats are alot more prone to things which need immediate treatment.
Failing that, I would just phone around and take the earliest appointment given.......however....in my case this would be after I had completely lost my temper with my own vet and almost deffinately ask him why he is working with animals when he obviously doesnt give a damn....animals aren't just a file u can shove to the back of a cabinet until a space becomes available! It took me a good few years to find a vet whom I was completely satisfied with...(and the few who didnt take too kindly to me speaking my mind! lol)