<p>Can anyone recommend a ready-to-use class/library compatible with C/C++/MFC/ATL that would parse iCal/vCal/Google calendar files (with recurrences)? It can be free or commercial.</p>

there is a
parser in PHP for iCal
, you can downloaded and check the code to suit your language.
for vCal/vCard parsing
there's a C Library
.
for Google Calendar I couldn't find any exact answer, so, try to Google it.