3.01 was the latest Lotus Notes C++ API toolkit revision number, but IBM also released versions that have 7.x and 8.x release numbers that correspond with the Lotus Notes/Domino releases that they supported.
You can find them here.
https://www-01.ibm.com/marketing/iwm/tnd/nochargesearch.jsp?k=ALL&S_TACT=105AGY79&status=Active&q=%22C%2B%2B+API%22
You'll have to download and check their documentation to determine if they are compatible with VS 2012. I haven't used those APIs in more than ten years.
-rich