Since hatching eggs is such a big part of progressing in Pokemon Go, and you only have one infinite use incubator... this means incubators are a pretty useful commodity. Can you ever receive them from Pokestops? And if so, what level do you need to be?
I don't believe that you can receive Lures, Incubators, Lucky Eggs, or Incense from Pokéstops, and that you must either purchase them from the store or receive them as a reward for leveling up. I don't have any evidence other than anecdotal at level 20 with 1000+ visited Pokéstops. If anyone has any counter-evidence please post it!
According to http://www.gamesradar.com/pokemon-go-level-rewards/
You get 1 incubator at level 6, 10, 15 and 2 incubators at level 20.
You can get incubators from pokestops. I received one (with three uses) a couple of days ago around level 4 or 5. Unfortunately, I didn't realize it was apparently a rare event or I would have taken a screenshot. It also has fallen off my journal or I'd screenshot that. They are out there!
The incubator is on its last use now so I was trying to check how rare they are from pokestops when I found this question.
Edit: I see now that you apparently get one from leveling up to 6. I was pretty sure I had it before then, but perhaps not. I don't have two, so if you 100% get one from leveling to 6 then it must be that one. Leaving this post for posterity anyway cause why not.
Can't say for sure, but this page from "International Business Times" says you can obtain Incubators from Pokéstops.