You could run a simple script like this:
#target indesign
// Carlsen
var doc = app.activeDocument;
var buttonNames = doc.buttons.everyItem().name;
var buttonNameArray = [];
for (var b = 0; b < buttonNames.length; b++) {
buttonNameArray[b] = buttonNames[b];
}
buttonNameArray.sort();
var f = File("~/Desktop/ButtonList.csv");
f.open('w');
f.encoding = 'UTF-8';
var l = buttonNameArray.length;
for (var i = 0; i < l; i++) {
f.writeln(buttonNameArray[i]);
}
f.close();
which just writes a list of names to a text file. If we use the extension ".csv", Excel can Open it and put all the names in the first column of the new spreadsheet.