Quite few of the STF huts have them for sale,e.g Kvikkjokk and some on the Kungsladen.You often find them left in the open Vindskidds,dont rely on them but they are useful to supplement your own.
If you fly into Stockholm you have time to pick up a cylinder if you are continuing by train...the nearest place to the station is a Naturkompaniet store...have a good trip.