Do you have the tilt or fixed screen? The buttons for the fixed screen unit can be bought brand new on eBay for just over $100. The tilt screen button is hard to come by, there's a seller on eBay who sells used nav faces with the buttons and knobs. They're a crapshoot though as most have wear on them. I watched for a while and he finally posted one with great buttons.
Just search "escalade nav radio buttons" on eBay and you'll see all the options.