In the year 1792, where was the headquarters for the “monseigneur” in Paris?

Did you mean in London? Tellson’s Bank in London becomes a “great gathering-place of Monseigneur".Here French nobility gathers to speak about the revolution and plan on how they can retrieve their assets. Tellson’s has decided to dispatch Mr. Lorry to its Paris branch to try and save their valuable ledgers, papers and records from certain destruction.