1. Can an ashkenazi buy new clothes that he would make shehechiyanu on during the 3 weeks but not wear them until afterwards? Would this be a problem for Weekday clothing to the likes of pants and buttondown shirts…
2. Would they require a shehechiyanu anyway?
Since now days the custom is not to make shehechiyanu when purchasing a new garment but only when wearing it, therefore new garments can be bought in the Three Weeks (before the Nine Days). A garment that is not important enough to make a shehechiyanu on can even be worn in the Three Weeks (before the Nine Days).
O:CH 551 Mishnah Berurah 45.