Chan, it might be worth you looking on the Emberton Riding Club facebook page. Quite a few of the members are based out that way and might know of something.
When I moved to the area about 2 months ago I posted on the local FB groups and people were so incredibly helpful, so definitely worth doing that. Its how I found my current lovely yard
I don't know how far your going but plum park farm (towcester) is good there is hacking through fields and roads and also a school 2 cross country fields and a show jumping field. Straw and hay is included with large turnout fields as well.
At East Lodge, the livery yard near Courteenhall not the riding school over the other side. I LOVE it! In 30 years of owning horses I've never been on such a lovely yard Its transformed horse owning for me! I'm still waiting to find out what the catch is, but I honestly dont think there is one