Unfortunately, there is no free tool that can provide a solution to the conversion part. However, there could be a possible way through Outlook. Install a trial version of the Microsoft Office package and load the file to Outlook. After this procedure, export the OST to PST file. The trial version won't have limitations, except that it can be used for a limited time.
Download Microsoft Office Outlook: https://products.office.com/en-us/try
Note: A LIVE or Microsoft account might be required in order to install the package.