Mono 3.10.0 is the latest version of Mono (released over the weekend); not 3.8.0
Weirdly, 3.8.0 is the "latest" news release on their page.
So while you can download and build the source for 3.10 right now you can not download the packaged mdk's as easily. At least it's not trivial to find them anyway. I'm not sure of why this is.