**As always, New Guinea to the Rescue!**

Turns out there are some isolated tribes on that island who have been isolated for a long, long time, 10-20 thousand years, in fact!  Here's a reference:  http://www.sciencemag.org/news/2017/09/islanders-new-guinea-are-some-most-diverse-people-world-here-s-why  (Note the link between isolation and diversity; makes sense, right?)

**Update**:  I'm emphasizing this genetic diversity point because the different highland types have been isolated from each other as well as the lowland guys on the same island, to hint that such a highland region could work out even if attached to a continent.

Their climate looks kind of like what you want, as the elevation mitigates the tropical nature of it.  Check it out...

[![enter image description here][1]][1]

More details here:  https://en.wikipedia.org/wiki/New_Guinea_Highlands#Central_Range_sub-alpine_grasslands  but the money quote is:

>  Above 3,000 metres elevation, the high mountain forest yields to remote sub-alpine habitats including alpine meadows, conifer forest, tree-fern (Cyathea) grasslands, bogs, and shrubby heaths of Rhododendron, Vaccinium, Coprosma, Rapanea, and Saurauia all quite different from the tropical rain forest that covers most of New Guinea.

>  The alpine habitat above 4,000 metres consists of compact rosette and cushion herbs, such as Ranunculus, Potentilla, Gentiana, and Epilobium, grasses (Poa and Deschampsia), bryophytes, and lichens.[ 2 ]

It even has the word "alpine" in it!  ;D  I can't promise you edelweiss, but work with me here.

Okay I know PNG is an island, but it's a *really big* island.  Does that count?

  [1]: https://i.sstatic.net/L0GZS.jpg