It can look like practically anything... I use grenade mags from the IG Cadian grenade launchers, painted with a red cross on a white circular field. Every one of my infantry squads has a 'medic' (counts as loader for the heavy weapon, actually).
George, for a start, this REALLY isn't a rules issue.
Second, take a look at the GW website, there's plenty of pictures of SM apothecaries. Check bits sites like warstore. Do a Google Image search for '40k apothecary' It's not hard.
Thirdly, Space Wolves don't even USE a narthecium, they use 'Potions and Balms' so any vials, bottles or little round bits should be what you actually need.
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