Matt,
I assume you are referring to B company, 25th Aviation Battalion. Here is their website: http://25thaviation.org/ Go to "Diamonhead" for B Company info
I checked there (they have tailnumbers from all their aircraft) and the Army Gold Book data and there is no ship listed with 426 in the serial that flew with the 25th. of course it could have been overlooked, but my guess is that the bird you flew in never actually flew with the 25th. Was it a UH-1H Huey? Do you have any photos of her from your flight? There are several UH-1D/H's with 426 as the last three digits of the serial so you really need the info from that bird I'm afraid. Any additional info about insignia on the helicopter would be helpful. Good luck with your search. The website should at least get you started as there are lots of photographs. Let us know how it goes.
Ray