You find many great playlists on the forum that you can import for free without registering on the forum. 
[If you are using an Android emulator, use the Forums window inside iReal Pro or a browser in the emulator. You can use your PC's browser to navigate, search, but you will not be able to import songs into iReal Pro]
In iReal Pro, tap on Forums and on the top of the screen "Quickly download Main Playlists" to import them. Here is an example on the iPhone:
Here are a few playlists to start with:
Click here to download the 6 main playlists.
You find detailed instructions how to import songs here.
In case you’re looking for a specific song:
On your phone/tablet:
tap on the Forums (globe icon), then the magnifying glass on the top right and type the title in the Google Custom Search field.
On computer:
Go to the iReal Pro Forum and on the top left, type in the title in the Google Custom Search field.
If you don’t find the song, you can post a question and maybe other iReal Pro users have it.