When I'm looking to learn a particular song I try to get the sheet music, my first stop is go to musescore, for a couple of reasons, the scores are free and they can be transposed to different keys, (all twelve keys) and then printed. I look at every key to consider which would be the most suitable key for a C 48 Chrome, (in my case all the flat keys and G). Sometime a 56 is the most suitable chrome, in my case rarely a 64 I never go that low. Looking at the sheet music can give me the note range on the chrome in any particular key so I can decide which key(s) might be the most suitable, once I've play the song in my chosen key(s) I choose the ones that to me, sound the best and can be played either the easiest or most effectively. Having said that I do try to play all my songs in multiple keys or at the least two.
Sometime song sounds best played in the tonic i.e. C. in my view if a song sounds really good in C play it in C, or the tonic of the chrome you are using. I've listened to a lot of great chrome players on Youtube and a lot of them will play a song in C, because it's the right key for the song.
Back to sheet music, if I can't find a piece of music on musescore will turn to Musicnotes, this is a pay site but it is really good; however, you have to pay for every print, so if you want the sheet in a number of different keys you have to pay for each print.
Just my thoughts on sheet music.