I often face the following situation:
I am reading a technical paper, and I can't figure out a calculation shown in the paper, whose details are not given. There is no reference in the paper about the exact calculations. It is not possible to get an answer from the author(s), either they are dead or they don't answer even if I did (even if they did, it takes a lot of time for them to respond). I can't write to my advisor; for him to help, he also needs to read the paper and practically this is neither ideal nor realizable in a short amount of time. I can't write to my friend because I don't have any friend who works in the same field as I do. I won't ask the question in one of the stack exchange websites, because it is often the question is too field-specific and technical that I don't receive any helpful answer in a considerably short amount of time (assuming that I will get a helpful answer, which is not the case most of the time).
So, in the end, I try and try to understand what the heck author did in that part of the article that I couldn't understand, and it takes a considerable amount of time for me to figure that out (if I can).
Question: Assuming that I am not the only one who faces such problems, where can we get help in such situations?
Note: I am working in a field of Physics.