Dave, this is an interesting question and subject.
I can see that you are a pretty accomplished musician. I'm afraid I can't think of examples of the kind you are looking for in particular, but it shouldn't be a hard thing to do if you have musicians who can play along with each other by ear.
I went to our site's video section, and punched in "mandolin" in the search box, and came up with this:
There looks like maybe a couple of examples of dulcimer and mandolin playing together in a group, but you'll have to look through them.
Sorry I can't be of more help!
Thanks much, I really enjoyed those and duh, why didnt I think of that.