Ironically, I have exactly the opposite problem, and single-handedly support the local tailor... A 38" inseam is going to be a tough find. Most unfinished dress pants have 37" inseams as their standards--which equates to a 36 with you add the cuff. Almost all designer jeans that I can think of finish their pants with a max 36" inseam. Otherwise, he might have to look for low rise pants or suffer from the wrath of high water...
I have a tall, thin guy, too, and he pretty much exclusively wears Levi's. The longer sizes can be hard to find, but it's not impossible. Their website has some helpful links.