Like Kaori said.
Storeitem (.Wil for image when its in your bag)
Ground (.Wil for image when on floor)
M-Weapon or WM-Weapon (.Wil for image on body)
If its anything like Mir 2, then Weapons is seperate to what other items look like on the body, Weapons have a totaly different .Wil file to theirselves, which include the look of each weapon in every direction used. Have a look through your .Wil files for that file.
From what Kaori said, im guessing its 'M-Weapon' or 'WM-Weapon'
Sorry if i'm way off, i'm not a Mir 3 man myself.
/Ash