Ordering one in will cost you a few hundred extra and yes, it does hurt your ability to negotiate - unless you're not fussy about delivery time. If you give them a few weeks, they'll be lever the next request THEY receive from another dealer and just trade from inventory. That way, they can avoid having to compensate the other dealer. At least that's how it works up here.
Or go to GM.com and search dealer inventories until you find one with YOUR car. I know that the GMCanada site works well this way - I know more about the inventory than the salesmen did. In the states, I think you have to go to GMbuypower to check out dealers' inventories. Hey, why wouldn't you?
Anybody else out there use buypower and can help evandro?