The only problem with getting replacement drums is that the original drums were swagged to the front hub, and finding people who still know how to do this and finding the correct swagging studs might present a problem. The wheel cylinders, linings, spring kits, etc. are all still available today from both Rock Auto or any of the local auto parts stores. Just do one side at a time so you have the other side to use as a reference. Before you start working on the brakes, first remove the brake drums, and then spray the old brake assembly with a solution of dishwashing liquid and water to loosen up all the grime and then either pressure wash or wash with a high-pressure nozzle on your hose. No need to worry about brake dust *asbestos) if you do this first. Your car originally had riveted linings, and you can still find NOS (new old stock) riveted brake linings on eBay. I just replaced the front brakes on my 1962 Chevrolet with riveted NOS linings that I bought on eBay.
Checking the Rock Auto website, they don't offer either front or rear drums. If there is an old auto parts store that still has a brake lathe, have the old drums turned and ask them to take a very light cut, just to clean them up.
I also checked O'Reilley Auto, and they don't list the drums. I did find that a pair of used drums did sell on eBay in September, so that is the best that can be done, is to watch eBay for some used ones, or contact one of the salvage yards in Arizona.
Update:
Search eBay for "NEW Front Brake Drum 11 x 2 1/2 , 1959-1964 Pontiac Fullsize 59 60 61 62 63 64" There is a seller that has more than 10 at the price of $99.99 and $20.55 shipping. I would buy a pair even if you don't need them right now, because in a few years, who knows if they will still be available?