Where in Paris is location of Mont de Piete? Do they still have regular auctions?

The Mont de Piété ("Mount of Piety") is also known as the Crédit
Municipal:

"Where I start, is the Crédit Municipal. This is also known as the
'Mont-de-Piété,' which was a pious foundation started in Italy, to
combat usury. It was widespread in Europe in the 18th century and was
introduced in France by Louis XVI in 1777.

This was suppressed, as a monopoly, by the Revolution and reinstated
in 1797. In 1860, it had 18 branch offices in Paris. From what I can
gather, it is, or was, the municipal pawn-shop."

Metropole Paris
http://www.metropoleparis.com/1998/330/330marai.html

"The Crédit Municipal de Paris, nicknamed « The Mount of Piety » or
more familiarly « My Auntie », held the first auction in Euro. On the
25 September, a lot of 142 musical instruments was on offer to
amateurs and collectors, in a place where people have been able to
come for over 464 years to pawn objects when they were in need."

Robert Schuman Foundation
http://www.robert-schuman.org/lettre/lettrean45.htm

Here you will find the address and telephone number, and a bit of
information about the auctions:

"Auctions: Surely the best potential deals. The professionals buy a
lot there. I never bought photographic goods that way. I knew well
Drouot (auction place of Paris for furniture and fine art): it is
always difficult to rival professionals.

Two public organizations sale regularly - to get information about the
sales :

Les Domaines 
17 rue Scribe 
75436 PARIS Cedex 09 
phone : 01 44 94 78 78 

Le Crédit Municipal de Paris 
55 rue des Francs Bourgeois 
75004 PARIS 
phone : 01 44 61 65 00 

both for gear in use - no collector items, which are sold in dedicated
auctions.To know if it is worth buying, one must visit the previous
sights to look at items before the sale."

Astronomie Photographie par G.D. Césari
http://perso.club-internet.fr/cesarigd/photoe9.htm

Here's the address and phone, as listed on Crédit Municipal's own
website:

Crédit Municipal de Paris
55, rue des Francs-Bourgeois
75004 PARIS
Tél : 01 44 61 64 00

Crédit Municipal
http://www.creditmunicipal.fr/contact_plan

An alternate phone number, and an email address, are here:

Tél 01 44 61 63 63
Email : contact@creditmunicipal.fr 

Crédit Municipal
http://www.creditmunicipal.fr/agences_permanences

Search terms used:

"mont de piete" + "paris"
"mont de piété" + "paris"
"crédit municipal" + "paris" 

I hope this helps! If anything is unclear, or if a link does not
function, please request clarification; I'll be glad to offer further
assistance before you rate my answer.

Best wishes,
pinkfreud

Good answer and almost immediate!