Wanted: exhaust adapter for sliding window for Whynter portable AC

I realized my windows are sliding and open from the side, so I need the exhaust adapter (part number ARC-WK-ADTR). The one I need is compatible with ARC-1030WN, ARC-1230WN, ARC-1230WNH. They seem to be sold out everywhere I look. Any help locating one for me to purchase is greatly appreciated!