I'm not having a lot of luck getting an answer for you.
Your ladder should have been made by Kemberly. To confirm the manufacturer, supposedly, you might find the name "Kemberly" embossed on plastic end-pieces. Their phone number was given in another forum as 800-346-2247 ext 229 or 230.
Finding an online website is another whole story. Kemberly's web site is "broke" (kemberly.com) They are a division of Atwood Mobile Products, Elkhart ( http://www.atwoodmobile.com/
). That is of course a part of a company called Creation from Chicago. Atwood, Elkhart lists a phone number of 800-862-3131 and 574-264-3131.
Good luck. I don't know the part number of your ladder. There are several used: MHL579 or MHL626 & there is likely others as well. Without a Kemberly catalog, your guess is as good as mine.
Good luck -