I know some of the local brewpubs sell kegs of their brews.
They are usually 5 gallon, 1/6th barrel kegs with a standard keg coupler. A few of the brewpubs may still be using the older twin-probe (aka Hoff Stevens) kegs. They don't fit as nicely in the fridge and require a different coupler but draft supply places can provide the necessary hardware if you need it.
The best I can say would be to call a place you're interested in.
For microbrewery beers, not every place will sell to the consumer (three tier laws and such) so you'd have to go through a liquor store. Binny's carries a selection if you call ahead but I also know of smaller stores in my area that carry craft beer and will order a keg given enough notice. I'm not sure what smaller liquor stores are in your area though. Again, the best I could suggest for a microbrewery (e.g. Half Acre or Metropolitan) would be to call or email them.