If you don't mind, we're answering your questions in a different order than the one you posed. But first, a little background.
Just as we found conflicting stories about the origins of crêpes suzette (QoD 11/07/05), it turns out the history of the margarita is similarly shrouded in mystery, with more than one bartender staking a claim and more than one Margarita in the mix, so to speak.
One version has it that a Dallas socialite named Margaret/Margarita Sames liked to invent cocktails for her friends -- who included John Wayne and Lana Turner in their number -- and happened to throw together some tequila, Cointreau, and lime juice during a 1948 Christmas bash, which allegedly lasted for two whole weeks, at her holiday home in Acapulco.
Another also places the invention in 1948, but holds that it was created in Galveston, Texas, by one Santos Cruz who invented it for singer Peggy Lee, who may or may not have downed the libation in one and then turned and asked him, "Is that all there is?" Or it was invented in the mid-'30s by a bartender named Danny Negrete at the Garci Crespo Hotel in Puebla, Mexico, who named it for his brother's fiancée, Margarita, on the eve of their wedding.
Danny subsequently moved and became the bartender at the Caliente Racetrack in Tijuana, which interestingly also lays claim to the accolade of having invented this fine beverage, as does Bertita's bar in Tasca, Mexico, and the Flamingo Hotel (adjacent to Mrs. Sames' party house) in Acapulco.
Then there's the account that attributes its invention to one Francisco "Pancho" Morales who is said to have come up with his version of the drink on July 4, 1942, in Ciudad Juarez, across the border from El Paso, Texas. Apparently, a customer came into the bar, named Tommy's Place, where Morales was working, and asked for a drink called a Magnolia. He didn't know how to make it, so he made something up and called it a "Margarita" -- the Spanish word for daisy. The story goes on to tell how he neither patented the drink nor boasted of its invention, and ended his days as a milkman in the U.S.
The most prevalent account, however, centers around a showgirl named Marjorie King who was allergic to/knocked out by (depending on which account you read) all alcohol -- with the fortunate exception of tequila. In spite of her affliction, she was apparently a regular at the Rancho del Gloria Bar in Rosarita Beach, Mexico, where sometime in 1947 or '48, she asked one of the bartenders, whose name was Carlos Herrera, if he could invent a cocktail for her using tequila. Herrera obliged by experimenting with different tequila cocktails, until he arrived at a recipe which Marjorie liked (and which evidently liked her). The chosen mix was hence named Margarita, the Spanish rendition of Marjorie.
So there's the background on the classic on-the-rocks margarita. As far as the mass-produced frozen variety is concerned, we can thank a Dallas restaurateur by the name of Mariano Martinez, who apparently invented the world's first frozen-margarita-maker on May 11, 1971, by modifying a soft-serve ice cream machine. They'd existed prior to this date, thanks to the electric blender (an invention from 1922), but this enabled overworked bartenders to mass-produce margaritas of consistent consistency (and quality). You can view Mr. Martinez's machine below or in the flesh at the National Museum of American History (part of the Smithsonian Institute).
Now to your question about where to get those 48-ounce "Margarita by the Yard" monsters (c'mon, this is Vegas -- no wimpy half-yards here). Here's the list of venues we came up with; please let us know if you've encountered any others and can remember where you were at the time:
On the Strip (where they average $15-$16 for house tequila)
