Amazon Essentials Men's Skinny-Fit Washed Comfort Stretch Chino Pant (Previously Goodthreads)

Amazon. Specifically, Amazon's "Essentials" line (formerly Goodthreads) has every waist/length combination you can imagine. Here's an example. Bonus is that uncommon sizes (like 28x34) are generally inexpensive and the "Essentials" line of clothes are generally high-quality. EDIT: Also, with those measurements you will mainly find pants in a Slim or Skinny fit. If your son spends a lot of time in the squat cage you're gonna need a tailor.