From what I've heard, you get those as a reward on some higher level guildleves. I haven't seen any myself, so if someone can confirm that would be great.
However, with beta ending in two weeks or so, I doubt you will be able to earn enough marks to "purchase" any abilities. :D
Yeah, and from what I've read, it's rather unpredictable whether or not you'll receive any; it seems to be quite infrequent and a little bit broken at present. I wouldn't worry about them much until the actual release.