UPDATE: We got in!!! As one person suggested, we got up early (for us) and just went to see the situation. It was totally fine not to have an advance reservation. There was a separate line for non-ticket holders and we waited a total of about 15 minutes. So happy it was that easy!!!!
Stupidly, I didn't book tickets in advance to Sainte Chapelle and we are in Paris now (April 2), leaving April 5, with tickets sold out until the 6th. My bad!!!!! Does anyone have any secret (but legal, of course!) way to get tickets? I did look for concerts that might be held at Sainte Chapelle, but the soonest one I can find is on Sat, April 6. Do they have ANY day of tickets, or any other route get tickets? Many thanks in advance.