JB_PT This is an interesting question, and I want to know the answer too, although it will be a long time until I benefit from it musically. I started with good old Wikipedia, which lists large works that include pieces in every key. WTC is on the list, of course, but I learned a lot of interesting things just by looking at the list. I hope not all of these works are as difficult as Liszt's Transcendental Etudes (which I've listened to many times, but never knew were all in flat key signatures!)
I'm going to keep digging, but here's the Wiki page.
https://en.wikipedia.org/wiki/Music_written_in_all_major_or_minor_keys
Just a few clicks and I've already found some dark reddit rabbit holes, and I've already gotten one virus warning. Walking on the wild side! I've found really cool stuff on other searches, so you never know what some shy Internet wizard will have hidden on a Dropbox somewhere. 😜