Why do you need to replace it? If it's dirty just clean it using the K&N Recharger Kit that includes the oil your filter needs. You can't just hose it off and expect it to work like it did when it was new.
If you need to buy a new filter because it was damaged, look into an AEM
replacement filter. If you can't find one, there are many filters on the market. Find one that fits in your fender area nicely and one that fits on the tube. Apex-i has a filter that has a filtered hole on the top that reduces turbulance inside the filter cone.