try ths http://www.learnsmallenginerepair.com/OILF.htm

your lawn mower repairs shops near you can't help you on this?

Kevin wrote:

hi. i currently own a hona 3813 lawn tractor. i need to replace the
oil and air filter and was wondering if anyone might know of a web site
that lists any cross references to these filters and other lawnmower
parts as the honda oil filter is $15 and the air filter is $50.

thanks