Looking for: Magner's (or other) cider in big bottles
There is an excellent selection of ciders at Liquor World in Porter Sq. In terms of local products, they carry West County & Farnum Hill, and they also carry a few european ciders, including a nice tart Basque cider. All in 750 ml (wine/champagne-style) bottle.
Oops, just saw the post above -- sorry! But here's a confirmed sighting.
Try the Wine Cask in Somerville (Kirkland & Beacon Streets and not too far from Porter Square). I have definitely seen the larger bottles of Magner's there (maybe 1L size). Plus they have a pretty good selection of other ciders as well including a number of the West County ciders.