K&N work perfect and better if you take care of them and use oil. I use foam filter oil on my K&Ns with no problems ever but if you need a unit filter the Sparks filter for hondas i believe fit
Any filter with a 4 1/2inch Inside Diameter will work. Filters off 04-08 YFZ prodesign intakes work also. The filter that comes with the sparks setup for the hondas work good to. Just google around.