Hi - have only just seen your thread.
We are in Brixworth but about to move up north - but can point you in the direction of a few local groups that I've gone to before (DD is just 2).
East Haddon - really nice small Mums & Tots group on Thursdays from 10am. At the cricket pavilion, up a little lane right oppose the Red Lion pub (you can drive up there).
Great Brington - mums & tots in the Reading Rooms on Thursdays from 10am, nice group but can be quite busy.
Brixworth - Rhyme Time in the library Fridays 9.45am, think there is then a surestart play session in the room above the library from 10.15 but I haven't been.
Long Buckby - Rhyme Time in the library every second Friday at 2.45 I think.
Have you seen the Toddle About magazine? I think it comes out quarterly and has listings of all local groups - also online I think here.
Can also really recommend a local baby swim class - Active Baby Company. Have taken DD to their lessons since she was about 10wks and she absolutely loves it. Really nice teachers, pools all over Nptonshire but one close to you would be the Barcelo Hotel in Daventry which is great. Could be a good way to meet others locally?
Hope this is some use and these are somewhere close to you. Not sure who your HV will be in that area but maybe they can help with some pointers?