Commission president France Charbonneau asked commission lawyer Simon Tremblay on Tuesday what had become of the cheque, which Antonio Accurso mentioned in his testimony last September.
Accurso said he gave the cheque to help Jacques Duchesneau, who was in debt after losing the 1998 mayoral election.
Accurso testified that Duchesneau told him he would get back on his feet after the electoral loss and that he would help him down the road.
Duchesneau, who was Montreal police chief between 1994 and 1998 and a member of the Quebec legislature from 2012 to 2014, has denied ever receiving the cheque and said Accurso's comments were completely false.
Accurso, meanwhile, has rejected the suggestion he mentioned the cheque because Duchesneau had been appointed head of an anti-collusion unit within the Transport Department in 2010 and had targeted Accurso in his testimony.
The commission previously asked Accurso to look for the cheque.
Tremblay told Charbonneau that Accurso's lawyer is still trying to track it down and that it might be in the hands of the Quebec Revenue Department.
The commission sat briefly on Tuesday to allow Tremblay to file some 420 items as evidence.
Some were additional information requested from various witnesses about their testimony. Some of the materials gathered will be made public in July, while some of the rest will be unveiled only when Charbonneau releases her report in November.