While sale.order might be referrenced from somewhere in the CRM module, it's stored in the sale module. I think you're looking for the sale.order model itself? You can find the definition here (in version 7.0, though I imagine v8.0 is similar):

addons/sale/sale.py

class sale_order(osv.osv)

Notice that the _name variable is "sale.order" which is probably what you want. If you want the actual DB table in postgres, it's simply called "sale_order".