Product review (3 stars): easy to order - do not last too long
Found this third-party replacement after trying to find the filters in the stores.  It fit just fine ... until it eventually crumbled after a year.  My factory filter was good for 4 or 5 years with yearly cleanings.  This one only lasted a year.  More expensive than buying replacement from Lasko directly, but I haven't see what they ship (I am sure not the one that came with it originally).

does the job.  Just buy several, one for each year.