I know all about tall skinny boys, since I have a close to 6'3" 147 lb beanpole who wears a size 13 shoe. Yes, finding clothing is difficult, but I have found luck with American Eagle online. They carry more jeans sizes, and also "T" (tall) for their shirts. My DS has long legs but also a long torso and arms, so those tall shirts have been a godsend.