What's the best way to earn CSC without paying by credit card? Is there another way to earn it? Quickest?

You can buy with sP, but it's really inflated right now due to the sale.

Right now, csc can only be generated if someone purchases it with cash. You can buy with sPs, but with the Black Friday sale, it is horribly inflated right now. You can also try and sell art, but people are using their csc for the sale and art probably isn't a huge priority for most people right now, with the sale and all. Your best bet would be to wait for next year's sale and save your sPs and purchase csc when the price comes down.