Assesing CGT on a farm!

I am currently preparing 60 odd acres for sale in Northern Victoria. The House and 5 acres is supposedly not subject to CGT but the balance of the land and water is. My accountant advises I need a valuation of the House and 5 acres at the date I purchased. Given the farm was originally 171 acres with house and water, has subsequently been subdivded and sold. How can I get a valuation on the house and 5 acres at the original time of purchase???

Thanks

Rowd's