I'm going to list US options, but I have a feeling maybe European lines or even South American retailers might be better for suits ( I imagine there are more tall skinnies there...and an appreciation for actual tailoring. Even if this is not true, let me hold on to this fantasy hahah)
J crew has talls for officewear such as blazers (pants are too short for me, but probably ok for 5'10" range) but run somewhat average to large (esp in tall sizes) rather than small/junior sized.
BCBG runs longer and carries smaller sizes. I use to own many skirts from them.....
Nordstrom members have free tailoring up to
100-300 bucks or so ( I go to Nordstrom Rack try to find the $$$$ suits that are super marked down and then alter). Even BP has some OK items at times for suits.
Banana republic..carries tall sizes but I haven't really shopped there forever....
I think Calvin Klein, Tahari, Jones New York make some ok sets that can fit if altered (JNY runs big though, you would need to probably alter a size 0)
However with department stores I have found it depends on store location though b/c there are better In STORE suit options in East coast. West coast clothing is mainly overpriced, chintzy and unlined craptacular assembles...sorry I went off on a tangent. But I halsoave same challenges with well made, fitting suits as well.....and what is called a "suit" these days......