HUD Textures - Blackmarket:

• guis\dlcs\ecp\textures\pd2\blackmarket\icons\grenades/tag_team.texture
• guis\textures\pd2\blackmarket\icons\grenades\outline/tag_team.texture

HUD Texture - In-Game (it's an atlas and not independent unlike Pocket ECMs/Leech Ampule):

• guis\textures\pd2/equipment_02.texture

As for the text strings, you can use Offyerrocker's Simple Localization Mod Template to easily change them via BLT. Specifically these:

name_id = "bm_grenade_tag_team",
desc_id = "bm_grenade_tag_team_desc",

So, it'll look something like this:

Hooks:Add("LocalizationManagerPostInit", "KF1MedicalSyringe", function(loc)
	LocalizationManager:add_localized_strings({
		bm_grenade_tag_team = "Medical Syringe",
		bm_grenade_tag_team_desc = "Cocaina, no flour.",
	})
end)

I've successfully replacered the gas dispenser.

Focusing on the images, what filters should I use (in GIMP) to replicate the style of the images?