There are a couple of options, neither of them particularly pleasant. First, you can copy the PST file, then on the copy, corrupt the TOC using a hex editor and use SCANPST to recover the copy to a third PST file. Your deleted calendar entry may be miraculously found there.
Or, you can pay for a commercial recovery tool. They tend not to be cheap. A couple of them have a free demo download, which will show you roughly what it can recover but not in detail.
Google will help you destroy the TOC, but I'm not going to go into it here and take the ensuing blame!