"Szaser" is the Polish Army's Chasseur-a-cheval type [upgrade 1 for "Polski_Rekrut_Lekka_Kawalerii."].
You're looking for "Recrue_de_Chevau-Leger_Polonais." (Troops.txt index #60).
They are considered French troops, so I'm pretty sure your Player Character has to be a member of (enlisted in) the French faction/army, in order to find them.
[You can certainly find their uniform at the French Military Depot.]
I recruited some in the village of Leczyca, the village of Praga, and at the Polish Military Depot ("Enlist them as Light Cavalry").
In some other villages, I got "Polski_Rekrut_Lekka_Kawalerii." [They, and "Polski_Rekrut_Kawalerii" are Army of Poland troops, with a different upgrade path].
So, the Game Engine may assign the "volunteers" that you get randomly, within the type class you select.
Anyway, I accumulated about 10 of each, before I decided to quit and report back to you.
[Yes, I cheated -- gave myself 2000 denars, so I could purchase them all. But, this was just for testing purposes].
Sometimes, because of how Docm has arranged the troop trees currently ("L'Aigle v.1.41"), if you are looking for specific troops, you have to look in BOTH the Regular (heavy?) Cavalry and Light Cavalry "trees."
You may not find them where you would expect them to be.
[Example - Russian Cossacks (the epitome of light cavalry) are in the Regular Cavalry upgrade path, as are Polish Army Uhlans, while your Chevau-Legers Polonais (and Russian and Austrian Dragoons) are in their faction's Light Cavalry upgrade path.]
As Inzunza says, "Heavy Light Cavalry." Go figure. Probably space requirements/troop tree "branching" opportunities dictated this.
But usually, Regular Cavalry Recruits upgrade to Dragoons or Cuirassier class/types, while Light Cavalry Recruits upgrade to Chasseur or Hussar class/types. (Austria also has Uhlans, and they got put in the Regular Cavalry tree, while the Dragoons were relegated to a "branch" of the Light Cavalry tree, as an upgrade to Chevaulegers, and no further upgrade).
Happy Gaming!
DARoot