AC/Heater box rebuild

Restoring my '72 Swinger and I am rebuilding my AC and heater boxes. This picture is not my box but I have this same opening at the floor vent. I dont remember ever taking this vent duct work off years ago when I disassembled my car so, I'm sure my car was missing this piece. Can anyone tell me where I can find one?

100_0480.JPG

Also, there are spring metal washer/keepers on the blend door actuator rods. I have broken 2 of them during disassembly. Can anyone give me a link to some suitable replacements?
IMG_2394.JPG