Welcome to the JavaRanch, Bash!
I do a lot of this lately, but I don't go mucking around in the
JSF internals. Since my backing bean is supplying the SelectItem collection, I just access that collection internally.
From what the JavaDocs say, the actual SelectItems are not directly part of their associated SelectOneMenu component. So to get them, scan the SelectOneMenu's child element collection, and look for SelectItem and SelectItems objects. If you find one or more SelectItems objects, you would then have to further enumerate them in order to get the individual SelectItem objects.