The closest script for a tactics battle system that I've found for Fire Emblem would be Gubids GTBS. The only problem is that it runs more along the lines of Final Fantasy Tactics instead of Fire Emblem. Although, many people have requested this kind of script, I don't know as though anyone has really taken the task. But I think that you could manipulate Gubids script so that it runs more like Fire Emblem...but you'd have to test it out for yourself. Sorry, I'm not a scripter...yet.