try IFAC. You should be able to find their number in the phone book.
I could certainly tell you who NOT to go for, but don't want to get into trouble for publicly naming him.
Anyway, despite what some of them will tell you, its not rocket science. You have your tax free exemption and you may qualify for what is called 'agricultural' relief or 'business' relief, which brings down the amount of tax payable.
If you get any of these reliefs though, you must continue to run as a farm for a defined period, that is you cannot rent the land or you change from a 'farmer' to a 'landlord' and the tax saved initially must then be repaid.