Hello,
I believe BlueGUI is still available to buy, and it still works as far as I know. Though as you said, it's no longer being updated.
I would recommend BBB GUI as its still being updated and has a few more features than BlueGUI. The link to the BBB GUI thread is
here. Also go the latest posts for the most recent version.
Quote: "Secondly, could I theoretically make a .dll in Visual Basic that would allow me to integrate these types of features for DarkBasic?"
Yes that is possible if you wanted to make your own DLL.