26" x 18" Wall Air Conditioner Mystery

[seasideheights]

I have a 26" x 18" GE Wall Air Conditioner in my kitchen. Although it's 25 years old & still runs great, I'd like to get a new one. Finding a 26" x 18" Wall Air Conditioner to fit in the same sleeve that's built into the wall now has been a challenge.

Does anyone know where I can purchase one?

[seasideheights]

The manufacturer of the 26" x 18" A/C is irrelevant. It doesn't have to be GE.

Thanks!