I am trying to replicate a certain paper, which derived an important formula based on five other papers.
In order to do a correct replication with insight into sources of error, I need to gather all five papers. However, ALL the methods I have used have resulted in nothing.
A typical answer would be "ask your librarian" or "ask the authors," however my librarian is famously incompetent (can't even speak English, and given the exact bibliographical data, found a completely irrelevant paper), and also it is realistic to assume all the authors are dead.
Now, in my replication work I have to say something like "I cannot estimate the source of error, because the original papers are lost."
How should I do this? I checked Academia StackExchange, but the closest search result asks about phrasing negative search results for papers on a particular topic, whereas I am sure that the papers exist. There is also this question about how to continue my literature search, but I am asking about how to proceed if the search fails.