Supermarkets carry a few dozen beers, usually rather boring, worth only if you are stuck in an area with no other options, which shouldn’t be your case.
In Como, check out Birratrovo and Birrivico.
Birratrovo doubles as bar and beerstore, they have hundreds of bottles and a small tap list of interesting and fast rotating beers. You can drink bottles at the bar too (you may need to ask to chill them first).
Birrivico is a bar, excellent taps, a fridge with 100+bottles and you can take them home if you want; the atmosphere is great. If you happen to be there late night near the weekend, check the bakery a few doors up on the same street that sells pizza slices and other things in the wee hours.
Near Como, you shouldn’t miss Birrificio Italiano.
For 20 years they consistently brewed one of the best Pilsners; but I usually loved also their Bock and many other beers; they have a barrel aging program and you may find something available (bottles can be purchased to take home); and on top of that it’s a great restaurant.
Something a bit different, Mamma Rosa (listed in the Places section too) is a restaurant, when I’m back in Como I always go at least once, long menu, great pizzas and fish, and they have a few beers from Birrificio Italiano and others, enough to put it on the map.