Fodor's Travel Talk Forums - Looking for a Private Guide for Paris.

On the search page (?), the second tab-like thing from the right, above, enter Michael Osman.

Somewhere among an abundance of posts will be his last known contact data.
He was our guide in Paris 20 years ago. He's probably pushing 60 now, but talent doesn't expire.
Of course, he may have retired from guiding, but it's worth your effort if you succeed.
Of note; he sort of interviews you, to find out what your interests are, so he can tailor your excursion.
So, if you're totally dumb about Paris, read a couple travel books, so you sound somewhat knowledgeable to him.
And, be open.
Somehow, without us saying we liked markets, he sensed/knew we liked markets, where did we meet him in Paris? A block from an open-air market. We walked thru it on our way to the first stop, but I could see he was making mental notes of things that interested us.