Where can I find basketball shorts for a tall, skinny teenage boy in south florida?

My son is 14 years old, 6 feet tall, and only 125 pounds, so he is really skinny. He needs basketball shorts for school but cant find any long enough that don't just fall off. Help?Where can I find basketball shorts for a tall, skinny teenage boy in south florida?
id try to look for some under armour armour compression shorts in clearance stores as marshalls or ross or just find some snug nike or adidas shorts.Where can I find basketball shorts for a tall, skinny teenage boy in south florida?
Buy some that can be tightened with a string. Ebay is all i have to offer

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