I doubt that any kanji characters commonly used in Japanese were made after 1946.
Some kanji characters used in Japanese are actually made in Japan. They are called 和製漢字 (わせいかんじ) or 国字 (こくじ). However, although I do not know when they were made, I guess that most of them were made before 1946.
JIS X 0208 regulates basic characters commonly used in Japanese for information processing on computers, and the first version was made in 1978 (it was labeled JIS C 6226 at that time). A later investigation by Hiroyuki Sasahara and other researchers revealed that the specification included twelve kanji characters which have no known origin. They are sometimes called ghost characters (幽霊文字; ゆうれいもじ). We can say that in a sense, ghost characters are kanji characters which were created recently (probably by accident), but they are by no means commonly used.