The Army Finance Corps has had the responsibility throughout the history of the military for distribution of the Mililtary Payment Certificates as well as the emergency notes used in WWII in North Africa and in the Pacific.
The Army Finance Corps museum is located at Fort Jackson, SC and though small has an abundance of information and displays.
Here are a couple pictures I took recently at the museum, note that they hold several cases of the series 691 and 701 that were never issued.
The two series of unissued Military Payment Certificates (MPC) were Series 691 and Series 701. The US Army held these two series until 1991, when the US Treasury demonetized (voided) both series.
At the time, the US Army Finance Center at Ft Ben Harrison held the entire collection. The Finance Center transferred the collection to the Center of Military History and the US Army Finance Corps Museum by 1993; which in turn moved it to a holding facility at Anniston, Alabama.
The Federal Government has never officially issued or released either of these two series, but there are small quantities that have "leaked" into the collector's hands.
For more information about U.S. Army Finance Corps Museum use the link below for the official website.
U.S. Army Finance Museum