You can get literally thousands of free DLC songs for Rocksmith. Very easy to do:
Perfectly legal too - you can’t use this method to get songs that have been officially released via Ubisoft - rather this is content made by other enthusiasts.
After getting it all working (link above) you can grab the songs here. (And you can apply filters - so if you only want songs with bass parts tuned in Drop D you can easily find them, etc).