03-04 Corollas are different because they didn't have the drive-by-wire throttle system, the 05 and up Corollas did have this feature, hence the reason why it seems like there are less parts available for them.
K&N is just a brand that makes filters, doesn't necessarily mean they will make a system for your car, there are other companies out there that make the whole system aside from the filters.
go to
www.cosmoracing.com if you're looking for one of their system, I believe they do have it for the 05 and up Corollas.
