Short answers: it's a requirement of sorts, it's probably acceptable (with caveats), mostly, assuming you have covered major databases and/or Google Scholar.
Long answers: One of the requirements for academic research, particularly in the context of dissertations, is to contribute to existing research. This can mean coming up with a new approach to solve a particular problem, or a new theory or idea. But it can also mean looking at a topic from a slightly different angle, or focussing on a different aspect.
Not all research (#notallstudies) has to be new and exciting. Trying to replicate and thereby confirm existing research is entirely valid and acceptable. However, the current publication process favours developing new studies and approaches over replication studies. A perceived lack of originality may therefore hamper your publication chances, which is problematic in itself. Whether this is an issue for you depends on your future career plans and choices.
Whether your slightly adjusted topic will be accepted also depends on how plausible it is that a different region / industry / sample composition would bring different results than the original study. For example, if you're looking at topics that are likely to be influenced by cultural differences / class / education background / or similar, you can reasonably expect that looking at a different country or a different sector may yield new information. However, there will be other factors where it would seem implausible that region or industry would have any bearing on them, e.g. left-/right-handedness, general IQ, neuroticism scores etc.
In checking for existing research you should make sure to cover relevant journals and databases in the fields. You're not expected to research the library of any university, but to cover relevant publications.
Lastly, a few caveats:
Check your university's requirements. Whatever I and other people tell you will be based on our experiences in particular contexts and institutions. Your institution's guidelines may differ.
Answers to your questions may also differ between subjects. My answer is based on experiences in psychology / social science research, particularly work and employment.