I heard from other users discussions that a certain amount of sP can be used to obtain CSC. Is this true?

There's no official conversion but you can buy cards from other users in the shop search.

Can you obtain these cards in any other way besides user shops?

buy them with real cash from the cash shop.

, I'd go with what is saying as that's the only way to get CSC on this site. I wish there was another way but alas there is not. :/

You can also sell items or artwork for CSC through trades.