I think this has what you are looking for, there are a few different cards to choose from but I think they are all in the 35mm square range (https://github.com/

I think this has what you are looking for, there are a few different cards to choose from but I think they are all in the 35mm square range (https://github.com/blues/note-hardware/tree/master/Notecard https://github.com/blues/note-hardware/tree/master/Notecard)