I know it's an old thread, but still...
– Normally, when CHKDSK deletes an invalid MFT entry for a given file, it moves the content of the file to a hidden “found.000” directory (or “found.001”, etc. when there are several) with a .chk extension. That is the first place to look for it.
– If nothing can be found there, and if R-Studio fails to find a specific file in raw mode, Photorec can do the trick ; although it is a freeware, it's generally excellent as a file carver, better than many commercial softwares, and on par with very expensive, professional forensic tools. If looking only for files of a specific type, you can uncheck the other types in the options, so as to reduce the unwanted clutter, and it can also reduce the chances of false positives and file truncation in some cases.
– Otherwise, indeed, you're left with the option of scanning the whole volume manually with a specific enough string, which is tedious but can save hours of work, as it probably did for the author of this thread. It's particularly tricky in a case like this because XLSX/DOCX files are compressed (standard XLS or DOC are not), so the actual contents are not readily apparent when examining data directly with an hexadecimal editor, and it's not possible to use a particular expression that you remember from the original content of the file you're looking for (it won't appear as such within the raw data stream). So indeed that was a smart workaround.
What I wonder is why that specific XLSX file was not detected by R-Studio like the others : even if that was 7 years ago and the program has been vastly improved in the meantime, if it was indeed able to find XLSX files in raw mode it should have been able to find all of them. Unless there are several possible variations for a XLSX header, and the lost file had an odd one – I had a such an issue when
attempting to recover MKV files from a HDD which was originally full of them, but the MFT had been completely wiped, and R-Studio could only find a few of them (Photorec performed much better in that case).