I have never watched Helsing, I’m guessing they stole my idea and have Van Helsing’s granddaughter fight vampires (All action franchises should become chick action franchises). I just looked up Seras Victoria on cosplay com. Most of the costumes were in Blue or Yellow and one was in Red (post vol 7). In each one it's the same, she is wearing a European style Military Tunic, it’s cut like a jacket but lighter weight than a full jacket sometimes called a shell tunic as it has no lining very similar to the tropical bush jacket. I have a British one in Tan that is really close except for the extra buttons they add around the Prussian collar (I like to put it on with my pitch helmet and talk like the hunter Von Pelt about to bag some hippies). A military shirt will have the same look except it is to short and no belt loops. Look for patterns for a military tunic or go to an army surplus store. You might be able to find a Tan one you can un dye then re-dye yellow or a Blue military shirt and if you buy two you can add extra length at the belt line. Also look in the Simplicity catalog (In paper or on the new fangled internet) they might have some civil war blouses that are close.
Von “Adding 500 Sq Feet to my store with Military costumes spanning 500 years (5000 if you count the Stone Axe heads)” Dan