For both locations the club secretary will send out more details directions and briefing notes on the Thursday evening before the shoot that weekend.
Cambridge gun club: Postcode CB24 8AH
You should approach from the west, try putting "Cambridge Gun Club" into your mapping app.
http://www.cambridgegunclub.co.uk/directions/
Romsey: On Google maps, search for Test Valley Clay Pigeon Club - postcode SO21 3BE gets you close although you need the north side of the road.
Kingsclere Quarry: Wolverton, postcode RG26 5RW will get you close although the entrance is on the A339. The following map and street view image should help you:
