Excellent, I have bought a few off of ebay, the LOC has many. I find Union captured flags every day, yesterday for an example in OR 12 I found this..
At Winchester on 25 May, 1862, the 21st Georgia took a flag from the "Bucktail" regiment. I dont know what regiment that would be.
The 6th La took 2 flags on 24 May, 1862.
On 6 June, 1862 at Harrisonburg, Virginia the 1st New Jersey Cavalry was ambushed and Col Percy Wyndham and 30 of his men and both flags were captured (OR page 676)
At the battle of Port Republic, the 5th Virginia "found on the field, a flag from the 5th Ohio".
Trimble's Brigade also captured a flag at Port Republic, but it did not mentioned who the owner was.
At the battle of Winchester on 25 May, 1862 the 33rd Virginia captured "A Stand Of US Cavalry Colors". Did not mentioned who lost it.
On 24 May, 1862 the 27th Virginia captured "a stand of colors" at Bartonsville (5 miles south of Winchester) in a skirmish.
At the battle of McDowell on 8 May, 1862 the 58th Virginia captured a "Union flag".
Front Royal, Colonel Kenly was wounded and captured and it mentioned that the 1st Maryland Regiment (USA) lost a flag and were cut to pieces along with the 1st Michigan Cavalry.
18th Georgia captured a flag from the 24th New York.
17th Virginia---11th Pennsylvania
Evan's SC brigade took "3 stands of colors"
42nd Virginia captured the a flag from the 74th New York of Taylor's brigade.
6th NC took the 56th Pennsylvania's flag
Hood's Texas brigade took a flag from the 10th New York
Now Hood reported that his division (his old brigade and Law's took 8 flags.) I have found only 2. (10th New York and 24th New York).
Since these Yanks dont admit to losing a flag that often. I usually checkout every Union regiment in say Hood's division's path at 2nd Manassas. I have the Union order of battle and then its just a checklist after that. I write the names of all the Union regiments and head on over to the LOC.
I definitely think the Union army lost alot more flags then history has said so far. I will be at the LOC this Saturday with my group.
I will be on vacation from August 18-25 and I will bring all my Union captured flags, over the last 15 years and do a complete reorganization.
It's not hard finding captured Union flags, the hard part is figuring out who they belonged too.
Thank you for the help, Gregg!