Go to the Browning website and look at there distributor list. You can begin by contacting them in your area. The 280 isn't listed as an available caliber. I have a friend that has one of the lightweight models with a 20" barrel in 280. Just because a particular cartridge isn't cataloged doesn't mean it isn't available. Go to some gun shows and you will find new non-catalog rifles all of the time. This is because most distributors that are willing to order enough rifles can have about anything that they want.

I personally own a Remington 700 Classic Stainless in 257 Roberts that was never a catalog item. My buddy also has a Remington 700 ADL laminate in 264 Win Mag that isn't a catalog item.

As for factory ammo there is more available today than at about any other time. Federal has introduced several new loads for 05 for the 280. Remington loads the accubond and core-lokt. Winchester has the BST and Fail Safe. Hornady only show the light mag which shouldn't be shot out of an auto. Overall the 280 is a fine cartridge and plenty capable for whitetail, mulie, pronghorn, elk, & black bear. As long as you choose the correct bullet for your application.