Its a Coupe, or to use it's original full name: a Champage Coupe. As you seem to be suggesting, you want glasses of this kind for drinking cocktails out of, rather than Champagne. And you're not alone.
Coupe's were the traditional choice for drinking Champagne, reaching a peak of popularity in the early 20th century. However they aren't really ideal for Champagne, as the large surface area encourages loss of bubbles, and fails to hold on to the aromas (whereas a Champagne Flute steers the lovely smells toward the nose more easily).
More recently, quality cocktail bars have reverted to using these Coupe style glasses in place of Martini glasses. This is partly because they are more practical than straight sided Martini glasses, that are easy to spill from. More importantly its been a way for craft cocktail bars to separate themselves from mass produced, syrupy cocktails, churned out in massive Martini glasses in mainstream bars. The Coupe has a more old fashioned feel (the Speakeasy trend has been around for a few years now, with few signs of dying out) and Coupe glasses tend to be small. The craft cocktailarians point out that a cocktail "served up" will warm up quickly, as by definition it doesn't have ice in it. So it's better to serve these drinks in small traditional glasses (so you can drink the drink before it warm's up) rather than the massive Martini glasses that are so popular in retail outlets.
A quick search for Champagne Coupe, should find you a few sources to buy from.