We have purchased this kind of item in the past and believe there is no other way to do so that is as simple and inexpensive as through Appliance Factory Parts.
Media (1 set) he2913
13x3x20 1/8"
He2910, 2911, 2912 hi density rigid media 13x3x20 1/8" o/s wh5bl (back)
Buy this part and as many parts as you like and pay only $9.99 shipping, within the Contiguous United States.