I bought a centrifical/turbo filter for around thirty bucks. It swirls the air and dumps the chunks at the bottom of the clear container. This one doesn't have any moving parts. The ones with the spinning cyclone are really efficient but cost a lot more. For the money, this is a real deal.
Look in the YP for industrial air filters. All you have to do is take off the helmet filter and put the cyclone on.
Have you used the new Google feature called Froogle? Check it out. You could type in the part number on your air filter and probably find an aftermarket one.
Tom