Don,

The links are making me hungry; thanks for sharing!
I could only find this:
http://www.buzzle.com/articles/sherry-vinegar-substitute.html<http://www.buzzle.com/articles/sherry-vinegar-substitute.html>
which isn't really Paleo.
I think for that small amount you could really be forgiven for 
suggesting one use it if they allow that for themselves.

Just a combined teaspoon of pureed blueberries and a few drops of lemon
and a dash of fresh grated pepper might accomplish a similar effect...{?}

Thanks again; great resources!

Diane H.