Need an icon for my app. Where do I get one?

It all depends really. Dribble is great for highest quality work. Then you have 99designs, when you want the whole bunch of concepts for the fixed amount - then that's your call.
And if you are on a budget, Fiverr is your place. But do not buy a logo for $5 - you can get some nice ones for $20-50 easily.

If you don't know any designers personally, I'd suggest reaching out to one on Dribbble.com. If they're open for hiring, you can contact them through that platform. You'll also get a good glimpse into what style of app icon you'd like. Hope that helps. :)

I know people seem to speak highly of https://www.launchaco.com/ . They also have launched where you can get free logo creation.