Grenadiers and such?

I was wondering how you can get the Grenadiers and Handgonnemen of the Alliance of Paneria? I kinda got inspired by the firearms from Princess Mononoke and thought I'd try em out. I thought they could've been Elite Troops or something, but it doesnt say anything about it in the info, only something called "Rahna's" is mentioned there.

Help would be appreciated! 

They are elite units. You can get them by rescuing them (from parties that have the as prisoners).

In the endgame as Gutts, if you create your own kingdom, you get your own troop tree. Most ranged troops (not elite, just regular ones) there are firearm troops.