... Griggs Notice Board is a good place to start and there are several groups such as "farmers free ads on Bodmin moor" for agricultural free ads in cornwall. What part of the county are you in?
My bro' mentioned Griggs NB to me recently: I checked it out - not the best site for easy searching for what you want. Not dissing it - it's worth a look, but the plethora of business postings makes it a bit of a chore searching through. As to your mention of "farmers free ads on Bodmin moor", I shall have to check that out!