In the weapon tiki, the model has a shader associated with it, you then have to find that shader to backtrack and find the texture associated with the weapon.
Both player and weapon models use shaders.
So if a weapon shader is "gun_muzzle"
You need to find the shader "gun_muzzle" and in that shader you will find the texture associated with the gun muzzle. textures are in pak5, shaders are in pak0 if I remember correctly. I think it's in a scripts folder. It's been a long time since I modded stuff with pk3's, but if you can upload your mod (or what you have of it), I should be able to get it working for you. Just include the textures for me, and I can create a shader and configure it for you.
I forgot to add, gun_muzzle might not be the name of the script itself. For example there could be a "universal" weapon script called something like weapon_shaders.shader
and then in that shader there will be a part that is associated with gun_muzzle
gun_muzzle
{
//stuff
}
Sometimes it can be a trial and error process, but either way, just send me what you have and I can help you out when I get home.