We need a dishwasher that is 23" wide x 28 l/2" high, x 23" deep. Is this possible to find?

I think the width is going to be an issue. There are smaller ones that are apartment sized that may fit. But not a full sized one. As you already know 24" width is a standard size. The debth and height should not be an issue however. It would be better if you had a little more height as it may be tricky getting it into the opening.