Looking for fresh-squeezed lime juice ( on the Peninsula)
Santa Cruz Naturals makes bottled pasteurized lime juice that I have seen in several grocery stores. If you don't want to squeeze the limes yourself using one of those presses bbulkow describes, or use a presweetened mix, this juice is totally serviceable for cocktails. Santa Cruz Naturals also makes bottled limeade, but I mean the 100% lime juice.
I know not your request, but if you've noticed at bars, they have those funny presses that look like a garlic press but are made for lemons, limes, and oranges (yellow, green, orange). They take half-limes, and the middle size (yellow) works great for lime and lemon. You can find them in mexican markets, andronico's, sur la table, etc. For bar and general squeezing use, these things polish off limes in no time - you can get a cup in a minute, easy, although not with the highest efficiency, but limes are cheap. I like squeezing this way because you get plenty of zest. Add in limes from the mexican market at 10 for a buck, and you've got a party.
Have you tried Tommy's margarita mix? It's flash pasteurized and sold in the refrigerated section. It is presweetened w agave nectar.
BevMo used to carry it, as well as some Whole Foods. For tequila shopping, check out Mi Pueblo in East Palo Alto and you can buy extra limes for your guests to squeeze their own if they want more acidity.