Random Seeds is the way to go. Keep an eye out for seeds in buds, and save them.
My personal experience has been growing indoors ONLY with Bagseed. It is the best way to learn to be honest, to test your setup, temps, RH, nutes, Training, PH etc etc etc
It's fun and you don't feel guilty if they don't come out as you expected. Depending on your available space. just pop and germinate a bunch of them. Let them grow and as soon as you switch to 12/12 ( in case of the photoperiods ) you'll see gender in a few days or weeks.
If you smoke weed, I ASSURE you that you will encounter seeds. Be patient. if not.. invest in some cheap photoperiods, wouldn't recommend autos as they are a bit more finicky ( could be wrong here too, haven't planted autos yet, and I'm talking only from common knowledge and the interwebs )
Let us know when you start, best of luck !
Ninja.