When I was a teenager, my music teacher always had a copy of the Real Book around. I went to a local music store and was looking through their music books when one of the employees asked, 'is there something I can help you find?' When I said the Real Book, he said, 'oh, we don't keep that out here'... he disappeared for a minute and came back with a copy from the back room. At the time, I felt like I had been admitted into a secret club.
I have a very clear memory of taking the subway to a random music shop in Boston near Berklee as a teenager that an older musician friend had told me about that had Real Books in the back. Went up to the counter and when I asked for it the person working there got real quiet, asking me what key I needed it in, and then ducked into the back to grab it. I think it was something like $45, which was a lot for 15 year old me in the 90s at the time. It definitely felt like a secret club! I loaned it out to a drummer friend in college and never got it back, I should ask him if he still has it.
And the good jazz musicians can play their instrument from the C version. Over time you learn to transpose on the fly. It's just 12 keys after all, and the melodies tend to be not that complicated anyway.
