Q. My son’s Bar Mitzvah is this year on Sivan 7. We here in Eretz Yisroel will be leining Parashas B’haalosecha on the following Sivan 12, while those outside of Eretz Yisroel will still read Parashas Naso (because Acharon shel Pesach is on Shabbos).
My father will be coming, im yirtzeh HaShem, from Canada for the Simchah. He will consequently lose Parashas Naso.
Is there anything that he need do, and what?

A. Yom Tov Kehilchoso (9: n. 42) quotes Horav Eliashiv zt”l ruling in a similar situation that although there is no factual obligation to seek or create a special minyan to read the missing parsha, it is better to do so. He also quotes a similar p’sak that Horav Dovid Feinstein shlit”a mentioned in his father’s name, namely that a Ben Chutz L’aretz does not have to read when in Eretz Yisroel the Seder Haparshios of Chutz La’aretz, rather he follows local customs.
Ratz Katzvi (O.H. 1: 3) adds elucidation by explaining that the reading of the Torah is not a individual obligation but rather a communal one. It is the tzibur that creates the requirement of K’rias Hatorah and we therefore follow them in their reading.
A similar ruling can be found in Halichos Shlomo. (16: n. 26, See also Betzel Hachochmo 4: 151, 1: 2.)
Horav Shlomo Miller’s opinion is similar; he also suggested that your father may read on the Shabbos prior to his departure (Parshas Bamidbar) by Mincha the complete parsha of Naso (only three aliyos; sh’lishi reads the rest of the parsha), if he finds a willing tzibur.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a