Legio V survivors?

[Jona Lendering]

Has anyone else heard of this claim?

No, it's new to me.

Does any other ethnic group claim descendancy from a specific legion?

Not that I know of; nor does Ritterling mention any such claim in his RE article on the legions.

Does anyone know of any sources that either refute or support this premise?

I visited Vlachs in Greece, near Almyros. They were blond (blonder than the people from the plain in any case), had blue eyes, and claimed they were descendants from Achilles' Myrmidons... I think it was just an invention to please the Thessalian Greeks. When I asked whether they had something to do with Wallachia, they said they did not know.