2 litre swing top bottles of Flensburger Pilsener on sale at Carvill's on Camden Street.
Trouble is, they're priced at e20 each; a four pack of 500ml bottles of the same is a tenner. Even the guy behind the counter admitted it was "not good value."
The mouths on growlers are generally wider than regular bottles, so I'm not sure how this would suit anyway. Still, may be worth considering.