Air conditioner return grille

Question

I'm having trouble finding A/C return grilles that fit Filtrete Ultra filters. The grilles supplied by my A/C contractor measure 1/2" short (the 20x20 is 19.5x19.5 internally) and the Filtrete Ultra is 19.75 square. Does anyone know of a brand of grille that is actually the dimension that it's supposed to be, without any of this 2x4 "close enough" size?Thanks, Rick DeBay