If you don't want to replace the handle with an "original" that will cost you $400, the next best bet is to get a modern RV latch, modify the door, and install it. You can buy a chromed latch, with a built in deadbolt for less than $40. You will have to cut the door some to accommodate the new mechanism, as well as the frame. The new latch will be smaller than the original, so you will also need to patch the hole left behind.
If you want such a replacement latch, with the patches, rivets, etc., included as a kit, I believe I have seen them offered by Inland RV for around $130.
I took the hardest route possible, and completely reskinned my door before installing the new latch. I don't recommend this route.