Over 80,000 foreign nationals work part-time in Japan’s three major convenience store chains, data collected by Kyodo News showed Wednesday, in a trend likely to continue amid labor shortages from an aging population. Foreign workers now represent around 10 percent of the part-time labor force across branches of Seven-Eleven Japan Co., Lawson Inc. and FamilyMart Co. convenience stores, according to the data. Wednesday marked 50 years since the opening of Japan’s first-ever convenience store — a 7-Eleven outlet in Tokyo’s Toyosu area — on May 15, 1974. Now seen as an indispensable part of Jap…