Is there any way to make old DLC available to buy again? I missed out a few song that I like and there seems to be no other way to play these songs on Rocksmith 2014. Specifically "Pumped Up Kicks". I tried the "CDLC" route but no success there, since the instructions for importing .dat files are very obtuse. At the very least, can someone direct me to an easy-to-understand guide for using the Rocksmith Toolkit. Cheers!

There's not going to be guides here for that. The rules didn't change for the original RS DLC once they were all delisted, so sharing of any official DLC is explicitly against the rules, even delisted stuff