Well your only misconception is that you've got the species backwards.
Indica is beautifully suited to indoor, while sativa grows tall and flowers slowly, so is grown outdoors in areas with long seasons.
The reason you find few seeds in danky bags is that they are indoor plants and commercial growers never keep flowering males in the same building as their grows- any seeds you DO find are likely the result of either rogue pollen coming in on the breeze, or a hermaphrodite male flower on a female plant. Those are actually feminized, but carry the possibility of becoming herms themselves.

Check out our sponsors on the main page. There should be some links to seed vendors there. Or google the term 'cannabis seeds'. You might have to look a while to find one that will ship to the US but they DO exist.