We had to replace the hinge and spring on attic stairs we bought at Home Depot about 10 years ago. From this forum I guessed that they were Century Attic stairs and went to their website- (www.centurystairs.com).
I emailed them because I couldn't find a model number. An agent emailed back and was very helpful- the model number is on the yellow warning sticker inside the door, way at the bottom on the right. I think ours was C-91, but it will be something like that.
The agent walked me through ordering the parts I need.
Thanks for the tip off that Home Depot sold Century Attic stairs!