Hello ... Just as Simple and Short Tutorial ...
1. Create new Entry's in the Item_Shape, easiest is, just copy one level of weapon and
set new numbers and path'es to new Textures ... !
2. Do it also in the Itemweapon.csv
But remember, the numbers havent to be exist already ! or you would get overflow error
I hope it got you on the right way ... if you need further help, just PM me ^^