Many are aware copper became a war essential commodity early on. So, likewise, did brass - which is an alloy of copper and zinc. In 1943, as a result of a study the army conducted in 1941 or 1942, Ol' Uncle - the other Ol' Uncle - coined pennies from a zinc-steel alloy as a conservation measure.
Furthermore, as a result of the same study, plastic buttons - olive drab green - replaced brass on the enlisted wool overcoat and millions were saved (I don't remember the exact amount but it was a tidy fortune and, true to form, Ol' Uncle simply squandered the money on other "necessities").
A tiny morsel of info I stumbled across while researching your inquiry: The manufacture and issue of distinctive insignia, then called unit crests, now referred to as "DI's", was suspended "for the duration." It seems the Army required approximately FIFTY-FIVE AND A HALF TONS OF BRASS annually to meet requirements for existing insignia.
The "duration' in this case was 2 August 1947 but the ban on manufacture of newly-authorized "DI's" (since 1943)wasn't lifted until 1951. Another one of those little gems of information that are not only interesting but worth every bit of what you paid for it.
Still working on your inquiry. You seem to be interested in locating the 893d's battalion standard. It's probably safe to assume tht it's long gone. It was constituted and organized in June 1940 and inactivated in February 1946. Its colors would have been returned to the War Department and stored in a warehouse somewhere.
When the unit was redesignated 893d Tank Battalion in 1953, the old colors would have been declared obsolete and discarded. However, in such situations, there's almost always someone on hand - a former member, a collector or buff - to rescue things like that from the trash can. I'm surprised some former member didn't find some way to take it home with him.
Call the reference desk at your public library. Ask for the toll-free number of the Base Locater at Fort Knox. Call the Base Locator and have them put you through to the Armor Cavalry Museum. If the standard, or even a replica, exists, it'll be there.