Does the Central Train Station in Stockholm have luggage storage lockers?
Swedish Rail has their own helpline. Why don't you try it?
Both the train station and the attached bus terminal have lots of lockers available.
Yes, the station has lockers. I'm not sure why, though, but the day I visited, all the lockers were in use by mid-day. I arrived fairly early, and had no problems, but when I returned to the station a few hours later, a line had formed for people waiting to get a locker. That people would form such a queue spontaneously says quite a bit about the Swedish national character.