only definite way I know is through your account on the website. seems kind of odd though. They force you to buy the points on the web but buy the items in-game... still, that's the only way I know of.
You buy them. Click on "My Account" in the upper right corner of your browser page, and there will be a field displayed called Cryptic Points on the right. There should be a button called "Buy More" where you can purchase them.