u/oatmeal-pizza

I have two Levoit air purifiers (model LV-H126). One has a broken control knob, the other (shown in the photo) has a cracked knob that will be broken soon. They just fit onto a D-shaft on the air purifier. These are obviously replaceable parts, but I don't know where to find them in the correct size. The vendor won't send me new knobs. These are 3/4" in diameter and the D-shaft is 1/4" along the flat edge. Any advice on where to find replacement knobs?