Translation:There are three chairs in this office.
"In this office are three chairs" sounds awkward, as would similar sentences like: On this desk are three books -- On this boat are four people -- On this windowsill are two cats. To my native (AmE) ear, it sounds like we should be contrasting something. For instance, "In THIS office there are three chairs, but there are six chairs in THAT one." So I'm not inclined to add this word order at this time.