Is Siebold's Fauna Japonica (1850) available online please? Contains e.g. Carbo capillatus Temminck & Schlegel, 1850.
It is on BHL, though (but as a part of Vollständigste Naturgeschichte der Vögel, not as a self-standing work); also here, but for your usual purpose, I think I'd use BHL. Plates are on Google Books, but access is US-only, and also here.Reichenbach 1862 Singvogel. Available anywhere online please? Not on BHL.
Can't help with this one. As you say it's still under copyright, thus the only place where you should really expect it is on the journal website. (Or in Google Books, but then in snippet view only).Neumann, O. (1934). Drei neue geographische Rassen ans dem paläarktischen Gebiet. Ornithologischer Anzeiger 2 (8): 331-334.
I don't find it either. But, if you need something, you can perhaps point to Fournel 1836 [here], who quoted the 1825 description verbatim.Zoothera aurea on p. 60 of Holandre, Annuaire de la Moselle (1825) - not on BHL, nor google books that I can find.