In a document entitled INGERMANLAND VS. RUSSIA, The Ingrian Volunteer Regiment, 1919 by Ted Koppel (published in 1984 by WEAPONS AND WAREFARE Publications, 218 Beech Street, Bennington VT 05201 , the Ingrian flag is described as:
 
 

and the coat of arms is described as

An excellent site giving the history of Ingermanland can be found  here .  This was sent to me by Juri Saija <juri@narvavesi.ee>.
 
 

Thanks to Eino Ingerman for the following picture:

Here are pictures of some postage stamps from Ingermanland