"p-nut" the life of me find anywhere that carries this size.
This is Turtle.
P-Nut , You need to go to a HVAC warehouse in your city and they will get you any size grill you want or filter to fit it. You tell them what size grill you want and they can order it for you. If you want a filter to fit any return air filter grill , they will order it in throw a way or in washiable or reusiable. they will be listed under Air conditioning wholesale or Air conditioning warehouses.
now when the grill measures 9.25" x 15.25" it is a 9.25" x a 15.25" and nothing more.
Also these wholesale warehouses will deal with customers on things like grills for buying stuff wholesale is not a big deal with service people and the warehouse selling to you. they will deal with you like anybody else on grills like this.
TURTLE