I recently decided to get a RTW tuxedo, for the rare occasions where I need one. My criteria were:
-black preferable to midnight blue
-peak lapel preferable to shawl; no notch lapel
-grosgrain lapels preferable to satin
-preferably no belt loops, though I could have them removed
-jetted pockets (really did not want to tuck in flaps or have them removed)
-unvented preferable to side vents; no center vents
-flat front pants preferable to pleated
It seems picky but I think by formalwear standards its also pretty basic. Really, it's a bread and butter single breasted tuxedo. I went to the major NYC menswear places - Brooks Brothers, J Press, Paul Stuart, and JoS. A. Bank. Nothing really fit the bill. Everything had either notch lapels, or more than one button, or flapped pockets, or a center vent, or a combination of those. The ONLY place that had what I was looking for was Suitsupply. Happily enough, it fit me great in the shoulders and waist, and just needed a little shortening. But it's weird that the classics menswear stores don't make a classic tuxedo, but a more trendy like Suitsupply does. It pretty much hit every criteria I wanted, except for it having side vents - and I suppose I can have those closed at a later date.
The only downside is no vest, but I think that will be the case with all RTW tuxedos. I may swing by brooks Brothers to see if I can convince myself that the lowcut vest separates match the black of the Suitsupply dinner jacket...