I've found the filter still sealed in it's bag. Part number 16952-447-015. According to CMS it's for a 250N, 400N, CB250RS, CM400, CX500, XL250, XL500 and XR500.
However it appears to be the right size as yours, with the exception that it's 10mm taller, 115mm as opposed to 105mm, which shouldn't be a problem. The rubber washer appears to be 16mm OD with a 10mm ID hole. The strainer tube appears to be 11mm OD.
