Not to be overly technical, but corny kegs that you are talking about are actually different from 5.25 gallon kegs that we call "bullets." Many microbrewers and even some macros keg their beer in 5.25 gallon kegs as well as 7.75 "pony" kegs.
If you are interested in getting smaller kegs with a larger selection of brews, visit
ratebeer.com and find a respected beer store near you.