Surely there are some of you out there with the very tall and thin sons. I’ve found jeans and pants (thanks, JCP, Old Navy Online), but DS would like some sweatpants or athletic pants and Iam having a hard time finding any anywhere! A mens size “Small” doesn’t work around the waist. Any ideas? Waist=28, 6’2. Thanks!
Wow, your son is even taller and thinner than mine (size 29/34).
I bought him great athletic pants at TJMaxx, will look up the brand when I get home but you may try to just explore what they have if there’s one in your area. I’ve also recently discovered Uniqlo, they have very nice khakis in appropriate sizes and may also have sweatpants but I didn’t check.
My yoga teacher is this size and claims the only pants that fit him are Lululemon. (I know they are much pricier than old navy).
My one nephew is about that size, 6’3" and 140 lbs, and has taken to wearing the waist of most of his pants down low to keep them from being floods.
Some men’s small should work. Try the running stores where that body shape is not unusual with brands like Avia, Asics, and Brooks. I wear 30x34" and my men’s medium Brooks fit great.
Try H&M, my lanky skinny kid finds pants there.
Non-US headquartered brands like H&M or Lululemon might have something for skinny, tall guys.
My son is really picky about his clothes in general - the way they look, feel, etc. Not too heavy, not too light! Not too loose, not too tight! 
My S is not as tall or skinny as your son - he is 5ft 11 and a 32 pant. BUT he has worn these Adidas athletic pants exclusively for the past three years or so casually. He gets a medium so I’m sure you could size down to small or x-small. Not sure about the length for you - especially if your S likes them especially long (my son doesn’t …not too short, not too long!)
https://www.amazon.com/adidas-Soccer-Pants-Medium-Black/dp/B01GP2Z7AY/ref=redir_mobile_desktop?encoding=UTF8&pi=AC_SX236_SY340_QL65&psc=1&qid=1542245353&ref=sxts_1&sr=1&th=1
Thanks everyone so far! @abasket thanks, He has worn Adidas in the past, before the growth spurt though. But the fact that they have XS and even XXS is hopeful. Smart to look at athletic brands or running stores that probably would be more for a trim or lean body shape.
I can’t say I’m going to invest in Lululemon as I think he is still growing! But will keep it in mind for the future! Will try H&M too, a couple of years ago that worked. He’s just taller now but the waist hasn’t changed.
Husband is about 6’ 6” now, and super skinny. I bought him athletic pants a few years ago from “For the Fit”. You can find them online. You can also try googling “Pants skinny men” or something like that, and find a few other clothing retailers for the real skinny amongst us.
Looks like 28" waist would be XS in Adidas, Asics, Brooks, Nike, and Reebok:
https://www.adidas.com/us/help/size_charts/men-pants_shorts
https://www.asics.com/us/en-us/clothing-size-guide
https://www.brooksrunning.com/en_us/mens-clothing.html
https://www.nike.com/us/en_us/sfg/mens-shorts-pants-size-chart
https://www.reebok.com/us/help-section-size_charts.html
But would be between XS and S in UnderArmour:
https://www.underarmour.com/en-us/size-charts
But then he may have to look for XS with tall inseam, which may be an uncommon combination.
My son has a 29" waist and a 36" inseam so I feel your pain! JCPenney is my go to for pants/jeans for him. Luckily he’s not too picky about brand names.
As far as athletic pants, I had to get medium sized Adidas soccer pants for him as the small (which worked in the waist) were too short. The waist was a little big but with the drawstring they’re manageable. Like @Magnetron said, my son has to wear them a little lower so that the pants are long enough. From what I found, Adidas only has tall lengths in their XL and bigger pants.
My son is 6’ and a size 28… he buys his pants (and has gotten sweat pants) at H&M.
Both my sons, both of whom are 6’ 4"/ 6’3" and about 150, do UniQLO a lot. A Japanese company, the clothing is cut narrower, and a little longer. The clothing is a little more stylish, and cheap. They like that they can have trendy, funky kind of fun clothes that fit. Old Navy, etc. just never even come close to fitting.