Originally Posted by DKB_SATX
I'm not 100% sure about your specific trailer, but most of the mid-70s Airstreams and Argosy trailers used a lock that isn't available new anymore, called a KT entry lock. There's one on eBay at the moment claimed to be new old stock for the low-low price of $425 (plus shipping.) I've seen some doors retrofitted with a different door latch that requires a patch panel on the hinge side of where the KT was because it doesn't fill the entire space, but I don't know if those kits are available or how much they cost.
The KT lock shown on ebay is the same lock that is on my 1976 Sovereign
. Maybe someone will confirm that it was on the 1977 as well. You can see it by searching ebay for KT entry lock. It should come right up. It sure looks new and I would say is a good price if you need one.
I had the lock on my 1976 replaced a few years ago with a rebuild lock after someone tried to break in. The rebuilt one was about $350.
Check with Inland RV and see if they have anything.