The bone yard of course if you can find one that has an old Caddie in it...Might be Tougher to find than one would think..
Another Source is your local parts house
(Like, Uggg! Dare I say it...?? Kragens, The "radio Shack" of the automotive industry! You Got Questions? We've Got Air Freshener Trees...Neon license plate frames...Tiger skin seat covers...)
On the "Help" tree...however these are mostly "Generic" GM type switches if your going for resto...But they will turn your lights on and off, Which will keep you from contributing to the delinquency of the Muni Court system... LOL....
Have you tried caddy daddy or some of the others? A google search will find dozens of caddy specialists. I know, I own a couple myself, and I work on the neighbors 66. I have no trouble getting parts for it, or the 41 and 59