There's one in what looks like a little hut but is actually a bank, I think, just across the road from the Flora. Used this last year, it was the first one to get topped up after the Bulgarian national holiday when we were there! Talk about desperate one night, didn't think to get cash out when we first arrived, just brought enough with us for a day or two. Thank God for being able to put drinks on my hotel room bill, otherwise we'd have gone thirsty one night!!