An advert in Farmers Weekly can be quite productive.
I know someone who did this recently. He spent £300 and got four offers
- 1200m grass strip but the owner changed his mind
- 750m grass strip but with 60ft trees at both ends and a 1.4% gradient
- 700m grass strip which needed some work
- 300m grass strip
The 2nd one was a "diversified farmer" (most are these days) who offered to clear a 20m wide strip of his crop for the runway, in return for about £4000/year in rent. One could have split the cost among a few people, probably.
Worth a try, especially in the West where not many people live
In general the countryside is packed full of 400m options, fewer 700m options, and very very few 1000m+ options.