This is the only thing I've found. Not sure if I'm missing something on another site (which I probably am). Fill me in though cuz i would like to bet on this.
There is a better option which is Fairlay, they have a market on the vote (yes @ 1.4) as well as a market for
"Greece will adopt another currency"
and
"Tsipras will resign as Prime Minister"
Generally Fairlay has better odds than Directbet, here is a review. Good luck!
http://bitcoin-betting-guide.com/bitcoin-sportsbook-reviews/fairlay-review/