Russians over at 4PDA have a thread dedicated to the phone, which hosts a number of firmwares, including stock-based ones. Here is the Calendar app extracted from the "Stock+" one, uploaded to my AndroidFileHost for your convenience. You can also get other files from the package in case you need them.
As validation, the version number of the ROM as extracted from
ro.build.description=U8666E-user 4.0.3 GRJ90 C40B935 release-keys
"B935" - matches your current ROM exactly.