I also use the free MuseScore and I have never heard of the Pro version until now.
Here is what I do when I want to put a cover song into Musescore.
I DL a MIDI version of the song and put it into Musescore, BiaB, and/or my DAW.. For instance the Cole Porter songs you want just google/bing
cole porter songs in midi. Here is one of the sites I found off of that search:
https://freemidi.org/artist-1509-cole-porterThere usually are free and not free MIDI versions of cover songs available. Some of the free ones are pretty good while others really suck, but all of the for purchase ones are really good.
Another option I use a lot is with fake books. I will buy a fake book and then get the BiaB version of that book from Note's music:
http://nortonmusic.com/There are just the chords in these disks. You have to play the lead but if you are playing single notes on your guitar the inexpensive monophonic version of Melodyne will convert it into MIDI. I think RealBand can do that also but I'm not sure so you might want to check that out if you are on a PC.
Good luck and I hope this helps.