One year at Xmas I ordered pants from LLBean, Land’s End and Gap for my 6’5 son. He didn’t like the older styling of LLBean, but has ordered from Gap online ever since.
@great lakes mom – I agree that you have to try a few options to see what will work. When son moved up from Gap boys’ size 20, I ordered from a few stores to see which brand/style he would prefer. After years of buying pants only at the Gap, he chose Old Navy, a store I never set foot in (b/c it is not conveniently located and they play really loud music).
Sierra Trading Post, Dickies, Patagonia all have 28 waist 34+ lengths.
Haven’t bought pants for my tall 6’3" son in years, but when I did have to buy them we got them online from American Eagle. Our local store did not carry 36" inseam.
I never walk into Gap or American Eagle. They always have free shipping deals and online discounts and the “good” sizes can usually only be found online anyway. In store it seems like all they have are 36/30 
Lands End and LL Bean have a very small selection of pants that they can hem to your inseam with small waist sizes. My 6 foot son has a 28 inch waist and a 35 inseam and its nearly impossible to find, but those stores have a few. Good luck and please let us know what you end up with so we can shop there too.
I’m 6"8 and finding pants is not that difficult. I wear 36*36 jeans. Levi Outlet Store is your best friend
Anyone have input on suits? S is a size 38, but even the long in most places doesn’t work for him (sleeves are too short) - he apparently needs an extra long. A couple of the places (Macys, Joseph A Bank) told us they didn’t have this in the store and to order online - but I couldn’t find the 38 extra long online on their websites. We did find a suit in 38L that sort of fit him at JCPenney. Bought that one since that was the best of all we saw 
Have you tried a slim cut style in a 40L? Maybe Express or something? My 6’2" kid is actually a 40R in an Express Photographer’s suit. Maybe a 38L would fit as well (or maybe my kid just has really short arms.) We had to take the arm up an inch and a half on the 40R
For suits, “made to measure” may be an option for hard-to-fit people.
Made to measure sounds very costly. My husband is 6’7" and sons are nearly that and all have been able to find suits off the rack (that may have needed some adjustment) at Jos. A. Bank and Brooks Brothers, Men’s Wearhouse. I seem to recall my husband has found things at Macy’s as well. I just looked at a suit coat he had on the chair and it is Jones New York. Too bad Jos. A. Bank or Macy’s didn’t work for you. Try Brooks Brothers.
S found a tailor and ordered two custom suits for himself in LA. H is thinking of getting himself one as well. S says they were about $400, but he couldn’t find anything that fit well and was appealing for him off the rack. In SF, the starting price for custom suits was about $600, so even with custom suits, prices vary somewhat.
I suggested to S that if he gets any more, he might want two pairs of slacks with one jacket, as it probably won’t cost that much more and will extend the useful life of the suit.
(S & H aren’t tall, but hard to fit, as they are thinner than the “average” American and have trouble finding fitted off the rack that fits properly.)
Just saw on a commercial that Jos. A. Banks is having a major sale this weekend- $119 suits, shirts 4 for $99, etc.
Like many others,we use Old Navy tall sizes for casual items- they even sell long length sweats. Express has nice long slim fit dress shirts and slacks for reasonable prices. Our tall thin sons also have nice fitting suits from Men’s Wearhouse.