I've found the easiest way to find things on Mouser is to start right at the beginning and break the part down using the multiple choices. For example, I started out with "Passive Components" then moved to "Potentiometers and Rheostats" and from there to "Trimpots". After that I just looked at pictures until I found the right one.
That last part can work against you though, always make sure to check datasheets. Sometimes they just put up a picture of a part in that class, but it could have a different style of mounting, etc etc.