Just use an OEM Honda one, although even the quality of those will vary, the current lighter blue thai made ones might not be as good as the older Filtech or the much older Toyo Roki. If you want the ultimate OEM filter then you can still get the S2000 specific filter (15400-PCX-004) which is larger in diameter with more and better quality filter media, and purportedly different bypass pressure. These were once always made by Toyo Roki in Japan but the one I have sitting in front of me was made by Filtech in the USA.