Congratulations on your first Airhead. There are usually a few cases in the classified section of Airheads, also Ebay. If cost is not an issue try these:
https://www.motomachines.com/krauser-classic-side-case-set?_vsrefdom=adwords&gclid=EAIaIQobChMI652gyJep5AIVDvDACh1gHggtEAQYASABEgJkUPD_BwE
The Siebenrock cases are available from many different vendors.

The mounting racks are rather universal for all Airheads with dual rear shocks.

You might want to find a rack online and mount that at home. Then ride to a shop or store that can provide the bags. The problem is shipping such a large item as bags can be expensive. The other good thing is that you get to see them fitted in place before you purchase.

Read all you can. On some years the seat has to be taken off the hinges. That is, the seat no longer has room to hinge open with the rack in place.

basically, unless you luck out and find someone with a set in a garage not being used, your only choice is to buy them new. unfortunately they arent cheap. Capital cycle sells Krauser bags and the mounts for them but its almost $1000 for the setup. I lucked out and a local guy actually found me and sold me a set of OEM , but that was truly a unicorn. Good luck.

I lucked out, maybe...

The bike came with a set of hard, fiberglass saddle bags. They are in pretty rough condition cosmetically but a quick inspection didn't find cracks or structural damage.. The bike came with a big fiberglass batwing fairing in a similar state. I have no plans to every use it. They are (were) black, with some of the original pinstriping visible but the gelcoat is very badly oxidized. They look like they were stored outside against a barn for many years. I'll disassemble them and see how much will buff out. I never worked on very old fiberglass. Restoring these to good condition could easily cost more than the $1300 or so for good reproduction mounts and the better looking (to my eye), more rectangular side cases.
I'll take some pictures maybe later on today and post them for discussion.

If you want the classic look, Craven is back in business. They also sell spare parts if you find an old set. Mine came with a set of Golden Arrows that I had re-painted and will be ordering some new hardware for over the winter.

https://www.craven-equipment.co.uk/index.php/luggage/category/32-panniers

If you want a period look, the old "tear drop" shaped Wixom Bags look good, but are not overly functional (IMHO) for long distance hauling. The Hepco Becker bags (similar to Krausers) are my favorite for being spacious and easily detached. I have a set of old Bates Bags on one of my bikes....they are more of a permanent mount. When traveling I found a set of CL1200 Bag Liner Luggage which fit the Bates bags well.....and have a set of old period Krauser Bag Liner Luggage for my Hepco Becker Bags. On a third bike I use a set of soft luggage from Nelson-Rigg.