Replacement for Ice Cap RSK 16 x 36

I need to cross-reference replacements for some a/c units made by a defunct company in Long Island called Ice Cap. Their (hot/cold) model was either a 12,500 or a 14,400 BThU unit measuring 16 x 36 inches.
Does anyone know any sources for cross-referencing modern units which will slot into the Ice Cap sleeve built into the wall? Or a n/g where someone might know please?
Ice Cap mentioned that THEIR units would slot straight into numerous other manufacturer's sleeves so the reverse must be true? (The only one I can find is an Islandaire which looks as old fashioned as the Ice Cap)

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