Try the used car dept at any Cadillac dealer (and some other dealers). They typically have a large box full of fobs. I get fobs for my Buicks and Cadillacs at local Caddy used car depts and at a large Chevy used car dept. Total cost is a pizza or a dozen tacos.
Keys = ebay. mykeyless-1 is my favor and least expensive vendor. Good people. Never any problems. Dealer will cut key for free; programming key is effortless. Dealer will explain. He might also program fob for free or show you how to program it also. Key cost is like $15 or so including shipping.
I have gotten free fobs from:
McCombs Pontiac Hyundai
The used sales mgr and a worker bee salesman at Ken Batchelor Cadillac said they don't have any--just about the time that I thought I saw their noses start growing. Talk about customer service and marketing. As a result of this, I have never spent a penny at Ken Batchelor, and I refuse to do so.
I spend tons at the other dealerships listed. I also treat them regularly to goodies.