Most Builders will allow you to be represented by your Realtor, however some of them are not in the MLS system as Erin and Ute mentioned.
I pulled Sacramento County tax records, for these Rancho Cordova statistics:
243 homes were built in Rancho Cordova Zip Codes 95742 and 95670 (208 were in 95742 35 were in 95670)
Of the 243 homes completed and made ready for occupancy in 2007 approximately 189 were transferred to buyers. 54 remain owned by their builders. In addition to the ones already mentioned, these include William Lyon Homes, JTS Communities, Tim Lewis Homes and US Homes.
Some of the homes owned by the builders are pending sales to buyers, some are complete and waiting for buyers. Some are being used as model homes.
The statistics do not include homes completed in 2006, nor do they include homes that are currently under construction, and not ready for occupancy.
Dividing 189 by 243 tells us that builders have sold 3/4 of the homes they completed so far this year (77.7%) The builders appear to have made the business decisions to sell, by offering considerable incentives and large discounts rather than hold too many completed homes in inventory.