To sort out:
Don Bucefalo: https://gallica.bnf.fr/ark:/12148/btv1b8437359q/f1.item.r=Th%C3%A9%C3%A2tre-Italien https://gallica.bnf.fr/ark:/12148/btv1b8437360c.r=Th%C3%A9%C3%A2tre-Italien?rk=1824043;2
Simon Boccanegra https://gallica.bnf.fr/ark:/12148/btv1b53117971z/f1.item.r=Th%C3%A9%C3%A2tre-Italien.zoom
Esmeralda: https://gallica.bnf.fr/ark:/12148/btv1b70009304/f1.item.r=Esmeralda%20opera.zoom
Falstaff: https://gallica.bnf.fr/ark:/12148/btv1b531873083/f1.item.r=Hohenstein.zoom and/or https://gallica.bnf.fr/ark:/12148/btv1b531590273/f1.item.r=Hohenstein.zoom
Le roi de Lahore (1877) https://gallica.bnf.fr/ark:/12148/btv1b531791095.r=Le%20roi%20de%20lahore?rk=536483;2
https://gallica.bnf.fr/ark:/12148/btv1b70012442/f1.item.r=Massenet%20opera.zoom
https://gallica.bnf.fr/ark:/12148/btv1b7001245g.r=Massenet%20opera?rk=2145933;2
Manon (1884) https://gallica.bnf.fr/ark:/12148/btv1b53187292r.r=affiche%20manon?rk=42918;4
https://gallica.bnf.fr/ark:/12148/btv1b8438388r.r=Manon%20opera?rk=21459;2
Le Cid (1885) https://gallica.bnf.fr/ark:/12148/btv1b531790982/f1.item.r=Massenet%20opera.zoom https://gallica.bnf.fr/ark:/12148/btv1b70000976.r=Massenet%20opera?rk=1781124;4 https://gallica.bnf.fr/ark:/12148/btv1b531790982.r=Le%20cid%20massenet?rk=42918;4 - High priority
Esclarmonde (1889) https://gallica.bnf.fr/ark:/12148/btv1b53187300h/f1.item.r=Massenet%20opera.zoom
Charles Cambon: : [1] [2], [3] full-colour images, e.g. [4], [5]
Best:
https://gallica.bnf.fr/ark:/12148/btv1b53117713m/f1.item.r=opera%20affiche
Les Huguenots https://gallica.bnf.fr/ark:/12148/btv1b8438000c/f1.item.r=Meyerbeer
Weirdest:
Auber (sure I missed some with him)
Audran
Bellini
Instead, do https://gallica.bnf.fr/ark:/12148/btv1b531169722/f1.item.r=Bellini%20Norma.zoom and https://gallica.bnf.fr/ark:/12148/btv1b53116971m/f1.item.r=Bellini%20Norma.zoom
Berlioz
Bizet
Bruneu
Chabrier, E
Charpentier
David, F. (think I missed some of his)
Debussy
Delibes
Dupont
Erlanger
Fevrier
Flotow
Gounod
Lalo
Lecocq (TONS more)
Litolff
Massenet
Massé
Messager
Meyerbeer
Offenbach (incomplete)
https://gallica.bnf.fr/ark:/12148/btv1b531873350.r=opera%20affiche?rk=21459;2
https://gallica.bnf.fr/ark:/12148/btv1b53167757m.r=opera%20affiche?rk=5815479;2
Perry
Pessard
Planquette
Puccini
Reyer (lots more available)
Saint-Saëns
Salvayre
Semet (& Georges Sand)
Strauss, J.
Strauss, R.
de Suppe
Thomas
Vasseur
Verdi
Wagner
https://gallica.bnf.fr/ark:/12148/btv1b53179090g/f1.item.r=opera%20affiche
Wormser