First off don´t start making projects especially big projects if you can´t provide all the resources and just have too hope for someone too create that resources for you, second i don´t really know if this is the case but this would be your first public map since you appear to be new to the forum, then no one knows you or your capabilities and then no one really cares for your project or its completion thus you are less likely to get a response, and third even if someone with the basic knowledge on how too replace the groms weapon with a bow then it would require an animation transfer which isn´t likely too succeed due too the bones of the archers being extremely diffirent and would not fit thus requiring a whole new set of animation which a rare few can do and even rarer few would do so i suggest you just give it up man.
Unless you have something more too offer, higher reputation and i don´t necessarily mean the score just for your work and your persona.
Just use the grom model unmodified and make him throw axes instead of a modified version with a bow, when you release the map and if anyone likes it theres a chance you will have what you want and then you can change it.