Howdy,
I can't find a K&N for the PS250 either. I had the thought of taking the paper element out, and fitting a cylindrical K&N to the inlet hose [remounting the box cover, but without the filter]. Haven't done it. Reluctant I guess.
Since I had a Leo Vince performance exhaust installed last month, I have been thrilled with performance and mileage [routinely 80 + mpg, with brisk take offs], so I doubt that a K&N will do anything for me. Besides, I got skittish about the warranty in removing the stock filter.
There you have it!
f