My house has a Mastercool evap cooler, to supplement the A/C units (I live in southwest ) and it works great, however the diffuser grill is a plastic POS that looks like it came out of a 1956 single wide Champion

The home improvement stores carry all sorts of registers, but nothing big enough (20x20) for a swamper.

Can anyone tell me where I can find a nice 2 way diffuser that's made of metal, ?