If coming from the north then head for the M1 Junction 14 and follow signs for Newport Pagnell. If approaching from the east or west then head for north Milton Keynes and then for Newport Pagnell
The grid roads of Milton Keynes are high speed dual carriageways and best avoided if you are arriving on a bike. Instead head for Newport Pagnell if coming from the north, Cranfield if from the west/south and Wolverton if coming from the east and from each of these then use the minor roads to get to Newport Pagnell.
The nearest stations to Newport Pagnell are Wolverton and Milton Keynes, both on the west coast main line. Milton Keynes will usually have Taxis available but whether they will take a bike is probably a gamble unless you arrange it in advance. Wolverton is not manned all day and usually doesn't have any taxis waiting. Although nearest to Newport Pagnell you would have to arrange a taxi before or on arrival.