I have to ask... Are they different from coupe windows? A local yard has several mid-80's Riviera's. Shipping would be more than the cost... https://www.google.com/maps/@34.655052,-79.5212806,761m/data=!3m1!1e3 That is ONE of his three yards. PM me if need.
Same glass, he can use a window from any model year 1979-1985 Riviera. Toronado or Eldorado glass also fits.
I found him one from a 1984 Riv coupe, but the code is NOT the same; His is 27-104; it is 27-14 on the coupe.
Try contacting one of the companies that parts out Cadillacs (Caddy Daddy or similar? I see them in the Hemmings Motor News); they’ll likely know if coupe and convertible E body are the same (I think they are) and likely have one from an Eldo. Patrick