Think we may have found it but will send along where to look for checking my work!
Parts catalog here
https://www.winnebago.com/Files/File...8/98wg35wp.pdf
Down in window, vent, and exterior door group and page 77?
Click this snip to get better view!
This may get you the correct door but then I also suspect that may not help too much on the older items as they become out of stock for new???
A check for the part may lead to some but I'm guessing a look at the frig for brand and model number and then calling salvage may turn up better results.
Knowing the older frigs, I know they used the same frig for lots of years and lots of RV, so there may be a better chance of finding the right door by using the brand and model rather than a specific part number. The Winnebago part number may look past lots of doors used on lots of different brand RV?
You may have a bear by the tail or it might be right around the corner.
Hope that may help start the search!