Best bet is take a day out driving down country lanes and find cow fields,, youll see other people doing what you are there for and if you see young lads about ask em, oi boys wheres the fucking mushie fields round here and theyll help
Im in kent and know of about 6 real spots and a few other sods im gunna be checking, its easy finding the fields just wait til it rains a night then get out early and hunt