Mine has a plastic non-locking hasp. The sewer door latches at the top and drops down to open. Is this the style you have? I got a terrific idea from Steve Reigel to put another door on the other side of the rig's back corner but had a hard time finding it.
If your door is like mine, it can be found or ordered from markariosrv.com. Just look or search on the web for a JRProducts ZE102. If you try and get it direct from JRProducts they do not sell to the public. Makarios RV is the source for their customers. I have had good luck with them and they have good prices. I hope this link works:
https://www.makariosrv.com/products/...ar-White-.html
Is this it?