IIRC, the Stanford 193 iOS programming did one of these. it's free and very well done. They actually record the in-class lecture and post them on iTunesU.
I've done many of these and can't remember which one covered this, but Stanford probably has one.
As far as GitHub goes, there's tons of stuff out there. I just got done bringing SWRevealViewController and SWRevealCell into one of my projects.
I download the code and run the samples. Then look at what the code is actually doing and find a way to work it into a project. Usually, I have to change their code to work correctly with my project.
You should look at several samples and how popular they are. Some are better than others. The RSS feed one that I use doesn't have the code for pics. So now I'm stuck having to use another one or writing my own.
There's a lot of site that group these together for you. Sites like:
http://www.appance.com/category/ios/idevelop/libraries-components/
Some books have great tutorials while other are more general. One thing to think about is using something that doesn't have good support or good tutorials.
I used MagicalRecord and when I read another book on CoreData, the book used it's own helper classes, so the book conflicted with what I was already using. Generally, when you use a book, it'll be for Apple's APIs and using any other might not be supported.
Another example that shows this problem:
I have table views that slide in from the side. The cells inside the table have their own slide out for "add edit delete" functions. I now want it to have a "tree view" A tree view show the headers and options to show the cells or hide the cells of the group.
This functionality comes from a different product, so I have to figure out how to make them work together.
The danger is that you can spend a lot of time going down a path that may never do the work you want it to do. They not only require great isight to how things work, they likely don't have good documentation on how to get them to work with other programs.
So you're kinda on your own. Keeping it simple, taking the time to know how the code works, and looking hard at the code you're downloading can save you quite a bit of time.