Vista - Unable to locate web-bank certificate file

I recently signed up to web-banking. This requires a .P12-certificate file to
be stored on my hardrive at a location of my choice. I configured it to be
stored in c:\users\>username<\documents. The banking works fine and reports
the file located in the chosen directory. However, the file itself can't be
located anywhere on the harddrive including "virtualstore" or "temp" folders.
Very strange. If I delete everything in internet explorer browser memory
including "settings stored by add-ons" the banking stops working, as it can
no longer find the certificate and I can't "show" the banking system the
location, as the file is invisible (I did that once and have now gotten a new
certificate file).
The question is: How do I locate this file, as I suspect it is not really
considered a file in Vista. I want to make a copy of it to a usb memory stick
to use on other computers, but that's hard when it is invisible.

Thanks in advance