They don't have a specific model number listed for the Spec. I believe it is like 33-3120 if memory serves. We have the same airbox as the SE so it may be listed under one of those. I bought my at Advance Auto parts for $40.
Go to b15sentra.net and do a search on K&N. I know that there is at least 1 thread that has the part number listed. People will say that its not a perfect fit or our car isn't listed......worry warts. It fits fine, it is a litttttle bit snugger than the OEM filter but it fits perfect.