Lanark doesn't do stage 4 exams. Gleneagles would be worth a look although personally I'd be tempted to head to Blackdyke, they tend to have a good variety of horses who tend to be out competing and aren't just older schoolmaster types. In between look at yards with a variety of horses although they may not have coaches that train with stage 4 in mind it will give you more experience of different types then polish up your exam technique at Gleneagles or Blackdyke.