This is a bit weird- I can confirm that Nitro 9 and Nitro 11 both have the extended selection of page sizes, but Nitro 10 doesn't have much in way of paper sizes.
In Nitro 11, you should be able to right-click on a page and go to Set page size, and under the More, you should be able to find both of those sizes.
You can select all of the pages and then right-click and Set Page Size to change all of them at once.
Hopefully this helps- if not, let me know.