There are very few DIY yards in that area, the only ones I know of are Limbourne Park in Mundon (they have a school but no winter turnout) or Tiptree EC which has fab facilities but is quite expensive (for DIY) & normally has a long waiting list. There is another DIY yard just up from Tiptree EC I cant think of its name, has a small school but there turnout is always flooded, depends what you are looking for.
Good luck!