There is generally plenty of parking around Martinborough.
All around Martinborough there are a network of roads that are available for free parking. Don't be frightened by the number of people parking way back on highway 53 coming into the town, drive on through and turn left or right at Princess street and you will find lots of kerbside parking within good walking distance of the town centre where the Fair is held.
Parking is also provided by a number of independent organisations primarily as fund-raisers for their group. These are set up in fields around town and are generally advertised by a sign at the gate or entrance. One is on Princess street North, another on Princess street South, There is also usually a parking field in Cork Street.