You can earn mithril from participating in the Summer Wars; the catch is your clan has to win. Since the Summer Wars will turn into an All Star War you have to make sure you'd be able to take on LB. If you want to keep participating in weekend wars that is. Also this competition gives double mithril, so better make sure you have the stats and can stay up 24hours. You can also earn mithril from regular wars; doesn't give as much as summer wars but you get some. In conclusion; you cannot buy mithril at the moment. The Devs will release when we can.