Hello Jeff,
There are only a couple of 50 footers on the DLS, if you search using the word undecorated, I can't remember seeing any ''plain'' cabooses at all.
Only other areas to look are on 3rd party sites, jointedrail, rrmods, etc, etc, for un-liveried boxcars, unsure about cabeese, they aren't my area of expertise, I'm afraid.......:hehe:
Cheerz. ex-railwayman.