I've never even heard of vapor barrier clothes, i need to pay more attention.
And I'm being serious!
No need to be shocked. There is only one easy to find source for vapor barrier clothing, based on a quick web search. Warmlite by Stephenson at warmlite.com. They use a special fabric that is said to be comfortable, a vapor barrier, and stretchy - key to comfort in next to body or very near body wear.
There may be several sources of vapor barrier sleeping bag liners.
My understanding is that more skill is involved in combining vapor barrier clothing and layers of insulation than just regular layers of insulation. Lack of skill could explain indifferent performance and the resulting low market volume.
It isn't a magic thing that you buy and everything becomes suddenly warm and comfortable and easy.
Ultralightweight backpacking is fairly skill based, and therefore isn't sweeping conventional backpacking gear out into the streets and gutters. It, too, isn't a magic thing that is quick and easy.