In absence of that, I suspect the easiest would be to use an email
client that can handle mbox files and then email them to yourself to an
account connected to Outlook.
Another way (but requires infrastructure) is to attach your own POP or
IMAP server to the mbox file, then connect to this server with Outlook,
then drag and drop into a PST-based folder. Again, this only possible
for you you have access to the appropriate infrastructure.
Hope this is useful to you. Let us know.
rms