There are actually a lot of options for buying local food. They break down into a few major sources:

It's literally impossible to get more local than food you grow yourself. This doesn't have to be a major production - it can be as simple as having a planter with herbs by the window in your kitchen. This page explores some of the options available for people living in Marlborough.

Local farms are what most people think of when they hear the words "Local Food". There are several varieties of farm in this area.

Small Farm/ Farm stand

This is the quinessential local food - a locally owned farm the sells its produce on the farm itself, or nearby.

Farmer's Market

Local farmers often transport their product to a central location on specific days.

Community Supported Agriculture (CSA)

In some areas, you can buy a membership to a local farm. By paying a membership fee up front, the farmer is assured of a livable income. In return, you get a share of all the food grown.

Nothing says that you have to cook your local food yourself. Most restaurants buy their food through national distributors such as Sysco, so you do lose the connection to the people who grew the ingredients. But you are supporting the restaurant owner, and you do have the ability to influence their decisions.

Yeah. It may be surprising, but you really can get some local food from your grocery store. I tend to shop at the Price Chopper, so this page is somewhat biased in that regard, but I am sure that other store feature similar items.

Some areas have a Coop which coordinates purchasing food from local farms and distributing that to coop members.

I've collected all the farms I know of within 10 miles of Marlborough (and few outside that area) and put them all on a Google Map. Check it out at this link:
http://maps.google.com/maps/ms?hl=en&ie=UTF8&msa=0&msid=116972168170408463255.00044b9f3e3e20550d616&ll=42.33972,-71.463296&spn=0.171803,0.300751&z=12
Please let me know of any discrepancies on this map.