Centaura is perfectly right.
I used to work for a friends concert production company out of Little Rock and the ONLY time i ever saw a tour with an SM was a theatrical show. Concert tours are made up of different "groups" that perform certain funtions. A lot of the equipment for productions for lighting, sound, band instruments, and the like are found locally and usually bring their own crew.
For example, when we did backline services for puddle of mudd, we brought OUR equipment and used OUR people (and a few people supplied by the venue) to set everything up on our end. Another company provided the lighting trusses while the conventional lighting (mostly source 4's) were already in the venue. Each group gets plots, diagrams, and schematics on where everything goes weeks or months in advance so a stage manager is never needed. Most stage plots will even show where the cables should be run and where they should be covered with a rug, gaff tape, or glow tape.
There are a few "roadies" (the most I have seen travel with the tour is about 6-8, but there is more on REALLY BIG SHOWS) who do travel ahead of the bands and assist with any equipment that does travel with the band, but these guys have done this same show 20 times before and know what to do. Most of the time there is a Tour Manager who arrives and makes sure everyone is getting their breaks, getting paid and makes sure everything is in order for the show, but they dont show up until hours after the load-in and, like the band, leave as soon as the show is over, and sometime before.
The closest thing you will find to being a stage manager in a touring act is for 1) it to be a play or musical, 2)become a tour manager, 3)be on the payroll of a company that offers services to tours or venues and be in charge of a certain function, or 4)be a Technical Director for a well-toured venue.
There just isnt the cohesion between the different facets of a production that would require a stage manager because each part of the show knows their job and goes in and gets it done without any supervision because they are all getting paid mucho $$$.
The best idea is to sign up to be on a load-in crew at a venue or production company to see if you would like it.