None of the ammunition for the Hunter's Handgun is present in the mod, as far as I could tell.

I found the recipe. You can find it in creative by giving yourself the item, pressing 'a' when hovering over it to put it in your saved items, and looking at it from there. I'll leave the issue open for now, since the item is still missing from the search feature in JEI.

They're present in the creative menu, but not JEI. Can't find a crafting recipe.