The committee believes it has been sent by Malcolm McKibben to the permanent secretaries of government departments.
Committee chairman Daithi McKay of Sinn Féin said: "I am keen to see that very soon because I am aware there are some efforts to stymie this inquiry."
No witnesses appeared at the hearing.
Most of the session on Thursday was held in private.
The committee took stock of correspondence it has been sent, including from loyalist Jamie Bryson, who claims to have information about the loan sale.
Sinn Féin MLA Michaela Boyle said: "Reading Mr Bryson's letter he is a person of interest and we did put out the call for anyone who may have factual information to bring that forward.
"We are not in the business of shutting doors on anybody. Factual information should be brought forward."
The committee agreed to write back to him, asking for any evidence "within its terms of reference".
The Law Society is due to appear next Thursday.
The Nama Northern Ireland loan portfolio was sold to the US investment fund Cerberus for more than £1bn last year.
Irish politician Mick Wallace has alleged that £7m was due to be paid to a Northern Ireland politician in the wake of the deal.
Mr Wallace told the Irish parliament the money had been moved for that purpose to an Isle of Man bank account controlled by the Belfast solicitor Ian Coulter.
Mr Coulter is the former managing partner of Tughans solicitors in Belfast and worked on behalf of the buyers in the Nama deal.
He said he had directed that money be transferred to the Isle of Man account for "a complex, commercially and legally-sensitive" reason.
He said no politician, nor any relative of any politician, was ever to receive any money.
BBC Northern Ireland's Spotlight programme has established the Isle of Man account was intended to facilitate payments to non-lawyers or deal fixers.

Damien 'Dee' Fennell made an application to Belfast Crown Court to amend his conditions so he could go to Co Donegal for a week.
The 34-year-old faces three charges for a speech he gave during an Easter Rising commemoration event last year.
Mr Fennell has denied the charges. He is due to go on trial later this year.
He was charged with encouraging acts of terrorism, inviting support for the IRA and addressing a meeting to encourage support for the IRA after speaking at the event in Lurgan, County Armagh.
His lawyer pointed out that Mr Fennell had been on bail "for a significant period without breaching his conditions" and that his client would adhere to any requirements, such as reporting to the GardaÃ­ (Irish police).
"He is not going to abscond," said a defence lawyer.
The judge granted the bail variation if a cash surety of Â£2,000 was lodged.
He also ordered Mr Fennell, of Torrens Avenue, Belfast, to report to GardaÃ­ in Donegal twice a week and said both the house number and phone number of his accommodation should be provided to police.
Stormont's finance committee has said it wants to see a letter the head of the civil service has written regarding the National Crime Agency's investigation into the NAMA loan sale.
[NEXT_CONCEPT]
A prominent dissident republican facing trial over charges of encouraging terrorism has had his bail conditions changed so he can go on holiday.