Last summer, Wilkinson’s Fine Goods, in Denton, received its biggest online order to date. Owner Clint Wilkinson, whose family roots go back six generations in this North Texas city, was intrigued by his new client, who purchased a massive array of custom desk mats, bootjacks, and cherrywood boxes with hand-tooled leather accents. “I was just like, ‘Holy crap,’ ” Wilkinson recalls. “He must be a politician or lawyer or something.”Not quite. Wilkinson looked up the buyer, a Utah resident named Austin Post, and realized that he was doing business with Post Malone, the popular rapper who was raised in nearby Grapevine. Wilkinson emailed him to explain that fulfillment would take some time because every item would be handmade. The two now exchange texts about everything from…