1) This idea that one does not make shehecheyanu in the three weeks, is not one of the laws of mourning, as even a mourner is permitted to make shehecheyanu. Rather, it is because it is a period of punishment and it is not right to say the words “Who made us live to this time!”. (Mishne Berurah 551)
2) If he has a new fruit which he will not find after the ninth of Av, and he cannot keep it until Shabbos as it will go bad, he may make shehecheyanu even during the week (Kaf Hachaim ibid)
