You got it. Anyplace that sells womens cosmetics. You might even find some at your local supermarket. If in doubt, ask your wife / girlfriend / sister / female co-worker, etc. How 'bout that cute girl over there? Might be a good conversation starter ....
I don't look for a particular brand, it's the color. (Some of the purple and blue pearls are awesome, and don't forget the white). You might have to do some searching if you have a particular color in mind. Greens and yellows are hard to find, though these sometimes show up around Haloween.
One thing I should mention - use a good quality laquer thinner. When I went to shoot the Pie Wagon, I first mixed it using some cheap thinner; after setting up the AB (about two minutes) the color and thinner had separated. Tried it again with some automotive laquer thinner and had no problems. When you find your color, get a couple of bottles just in case.
"Trust no one; even those people you know and trust." - Jack S. Margolis