Might not be an appropriate question for r/askhistorians, but just thought I'd ask. Thanks!
Perhaps obvious: have you asked a librarian?
ProQuest hosts the Nineteenth-Century Short Title Catalogue behind a paywall. I don't have access, so I can't tell you for sure, but I imagine it would at least list a text's editions, which would give you a start towards figuring out numbers of copies. It's possible it could have more? Certainly worth a shot if you have access.