I take pictures of scenery I want, especially since I live in the city, or I look up traveling sites and find awesome looking places. I then take the picture of whatever I need, paste it into Manga Studio, and trace over it with the line tool. All the hard work of design is done, although inking at the pixel level can be a work of its own. The cool thing though is that you can take pictures of local scenery and do outrageous stuff over top to keep things nostalgic.
For my comic DeathCall I took a picture of a bridge from different angles and traced over it, the same with the bike. After that, I just had to shade it and ink it.
(Although, I'm hoping to learn from this as well to be able to make my own backgrounds. The middle, free-floating panel with the guy standing on the maintenance walk I did without using the paste method)
Hope that encourages those who have trouble with backgrounds to get better and find some awesome scenery, even in their own backyard.